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National Lakes Assessment 

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° A Collaborative Survey of the Nation's Lakes 


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U.S. Environmental Protection Agency (USEPA). 

2009. National Lakes Assessment : A Collaborative 
Survey of the Nation's Lakes. EPA 841-R-09-001. U.S. 
Environmental Protection Agency, Office of Water and 
Office of Research and Development, Washington, D.C. 
April 2010 


Library of Congress 



2011 505862 


This report was prepared by the U.S. Environmental Protection Agency (EPA), Office of Water 
and Office of Research and Development. It has been subjected to the Agency’s peer review and 
administrative review processes. This document contains information relating to water quality 
assessment. It does not substitute for the Clean Water Act or EPA regulations, nor is it a regulation 
itself. Thus, it cannot impose legally binding requirements on EPA, States, authorized Tribes or the 
regulated community, and it may not apply to a particular situation or circumstance. 


Cover photo of Emerald Bay on Lake Tahoe courtesy of ©Ted C. McRae http://beetlesinthebush.wordDress.com 











Acknowledgements 


The EPA Office of Water (OW) and Office of Research and Development (ORD) would like to thank 
the many people who contributed to this project. Without the collaborative efforts and support by 
state and tribal environmental agencies, federal agencies, universities and other organizations, 
this groundbreaking assessment of lakes would not have been possible. In addition, the survey 
could not have been done without the dedicated help and support of enumerable field biologists, 
taxonomists, statisticians and data analysts, as well as program administrators, regional 
coordinators, project managers, quality control officers, and reviewers. To the many participants, 
EPA expresses its gratitude. 


Collaborators 

Alabama Department of Environmental 
Management 

Arizona Department of Environmental Quality 
Blackfeet Tribe, Environmental Program 
California Department of Fish and Game 
California State Water Resources Control 
Board 

Pueblo de Cochiti Department of Natural 
Resources and Conservation 
Colorado Department of Public Health 
and the Environment 
Connecticut Department of Environmental 
Protection 

Delaware Department of Natural Resources 
Eastern Shoshone Tribe and Northern Arapaho 
Tribe, Environmental Program 
Florida Department of Environmental 
Protection 

Georgia Department of Natural Resources 
Idaho Department of Environmental Quality 
Illinois Environmental Protection Agency 
Indiana Department of Environmental 
Management 

Iowa Department of Natural Resources 
Lac Courte Oreilles Band of Lake Superior 
Chippewa, Conservation Department 
Lac du Flambeau Band of Lake Superior 
Chippewa, Tribal Natural Resources 
Department 


Leech Lake Band of Ojibwe, Division of 
Resource Management 
Maine Department of Environmental 
Protection 

Maryland Department of Natural Resources 
Massachusetts Department of Environmental 
Protection 

Michigan Department of Environmental 
Quality 

Minnesota Pollution Control Agency 
Mississippi Department of Environmental 
Quality 

Montana Department of Environmental 
Quality 

Nevada Division of Environmental Protection 
New Hampshire Department of Environmental 
Services 

New Jersey Department of Environmental 
Protection 

New York State Department of Environmental 
Conservation 

North Dakota Department of Health 
Ohio Environmental Protection Agency 
Oklahoma Water Resources Board 
Oregon Department of Environmental Quality 
Pennsylvania Department of Environmental 
Protection 

Pyramid Lake Paiute Tribe 
Rhode Island Department of Environmental 
Management 



National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 




Sisseton-Wahpeton Sioux Tribe, 

Environmental Program 
South Dakota Department of 

Environment and Natural Resources 
Spirit Lake Nation, Tribal Environmental 
Administration 

Tennessee Department of Environment and 
Conservation 

Texas Commission of Environmental Quality 
Turtle Mountain Band of the Chippewa 
Indians Environmental Program 
Utah Division of Environmental Quality 
Vermont Department of Environmental 
Conservation 

The following people played a pivotal role and lent their expertise to the data analysis of this 
project. These individuals painstakingly reviewed the dataset to ensure quality and consistency. 
These NLA analysts included Neil Kamman (lead, on detail from VT Department of Environmental 
Conservation), Richard Mitchell, and Ellen Tarquinio from EPA Office of Water; Phil Kaufmann, Tony 
Olsen, Dave Peck, Spence Peterson, Steve Paulsen, Amina Pollard, John Stoddard, John Van Sickle 
and Henry Walker from EPA Office of Research and Development; Donald Charles and Mihaele 
Enache from the Academy of Natural Sciences, Philadelphia PA; Charles Hawkins from Utah State 
University; Alan Herlihy from Oregon State University; Paul Garrison from WI Department of 
Natural Resources; Jennifer Graham and Keith Loftin from U.S. Geological Survey, Lawrence, KS; 
Jan Stevenson from Michigan State University, and Julie Wolin from Cleveland State University, OH. 

Contributors 

EPA would also like to thank those people who lent their scientific knowledge and/or writing 
talent to this report. 

Steve Heiskary, Minnesota Pollution Control Agency, MN; Neil Kamman, Department of 
Environmental Conservation, VT; Terri Lomax, Department of Environmental Conservation, AK; 

Alice Mayio, EPA Office of Wetlands, Oceans and Watersheds, Washington, DC: Amy Smagula, 
Department of Environmental Services, NH; Kellie Merrell, Department of Environmental 
Conservation, VT; Leanne Stahl, EPA Office of Science and Technology, Washington, DC. 

The National Lakes Assessment survey project was led by Susan Holdsworth (OW) and Steve 
Paulsen (ORD) with significant programmatic help from Sarah Lehmann, Alice Mayio, Richard 
Mitchell, Dan Olsen, Carol Peterson, Ellen Tarquinio, Anne Weinberg, and EPA Regional Monitoring 
Coordinators. Contractor support was provided by Computer Sciences Corp., Dynamac Corp., 
EcoAnalysts, Inc., Great Lakes Environmental Center, Inc., Raytheon Information Services, 

TechLaw, Inc. and Tetra Tech, Inc. 


Virginia Department of Environmental Quality 
Washington Department of Ecology 
West Virginia Department of Environmental 
Protection 

White Earth Band of Chippewa, Natural 
Resources Department 
Wisconsin Department of Natural Resources 



National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 




Additional Reports and Information 

To augment the findings of this report, EPA is providing several additional reports. The first 
is the National Lakes Assessment: Technical Appendix. This appendix describes in detail the 
data analyses and scientific underpinnings of the results. It is intended to aid States and other 
institutions who would like a more in-depth explanation of the data analysis phase with the possible 
intention of replicating the survey at a smaller scale. Additional results are also forthcoming. Due 
to a number of reasons, EPA is not able to report at this time the results from several indicators 
(e.g., sediment mercury, enterococci, and benthic macroinvertebrates). Work is on-going for each 
of these indicators and results will be published when complete. The Technical Appendix, Field 
Methods and Laboratory Protocols are currently available on EPA's web site at http://www.epa.gov/ 
lakessurvev/ . 

For those wishing to access data from the survey to perform their own analyses, EPA has made 
flat files of the data available via the internet at http://www.epa.gov/owow/lakes/lakessurvev/ 
web data.html . Additionally, raw data and information on the sampled lakes will be uploaded to 
EPA's STOrage and RETrieval (STORET) warehouse at http://www.epa.QQv/STORET . 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 









Table of Contents 


Acknowledgements.• 

Collaborators.i 

Contributors.ii 

Additional Reports and Information.iii 

Tables and Figures.vi 

Executive Summary.viii 

Chapter 1. Introduction.2 

A Highly Valued and Valuable Resource.2 

Why a National Survey?.2 

The National Aquatic Resource Surveys.3 

Chapter 2. Design of the Lakes Survey. 8 

Areas Covered by the Survey. 8 

Selecting Lakes. 8 

Lake Extent - Natural and Man-made Lakes. 11 

Choosing Indicators. 12 

Field Sampling. 14 

Setting Expectations. 15 

Chapter 3. The Biological Condition of the Nation's Lakes.20 

Lake Health - The Biological Condition of Lakes.20 

Stressors to Lake Biota. 25 

Ranking of Stressors. 31 

Chapter 4. Suitability for Recreation.36 

Algal Toxins.36 

Contaminants in Lake Fish Tissue. 39 

Pathogen Indicators.40 

Chapter 5. Trophic State of Lakes. 44 

Findings for Trophic State. 45 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 































Chapter 6. Ecoregional Results.48 

Nationwide Comparisons.49 

Northern Appalachians.52 

Southern Appalachians.54 

Coastal Plains.56 

Upper Midwest.58 

Temperate Plains.60 

Southern Plains.62 

Northern Plains.64 

Western Mountains.66 

Xeric.68 

Chapter 7. Changes and Trends.74 

Subpopulation Analysis - National Eutrophication Survey.74 

Subpopulation Analysis - Trends in Acidic Lakes in the Northeast.76 

Sediment Core Analysis.76 

Chapter 8. Conclusions and Implications for Lake Managers.82 

Overall Findings and Conclusions.82 

Implications for Lake Managers.84 

Chapter 9. Next Steps for the National Surveys.92 

Supplemental Reports.93 

Tools and Other Analytical Support.93 

Future National Assessments.93 

Acronyms.95 

Glossary of Terms.96 

Sources and References. 100 


l 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 




























Tables and Figures 


Table 1. World Health Organization thresholds of risk associated with 

potential exposure to cyanotoxins.37 

Table 2. Percent of U.S. lakes (natural and man-made) by trophic state, 

based on four alternative trophic state indicators.45 

Figure ES-1. Biological condition of lakes nationally and based on lake origin.ix 

Figure ES-2. Extent of stressor and relative risk of stressor to biological condition.x 

Figure ES-3. Proportion of national eutrophication survey (NES) lakes that exhibited improvement, 

degradation, or no change in trophic state based on the comparison of the 

1972 National Eutrophication Survey and the 2007 National Lakes Assessment.xi 

Figure 1. The process of lake selection.10 

Figure 2. Location of lakes sampled in the NLA.11 

Figure 3. Size distribution of lakes in the U.S. overall and for natural and man-made lakes.12 

Figure 4. NLA sampling approach for a typical lake.14 

Figure 5. Reference condition thresholds used for good, fair, and poor assessment.16 

Figure 6 . Assessment of quality using the Planktonic O/E Taxa Loss and Lake Diatom Condition 

Index.24 

Figure 7. Phosphorus, nitrogen, and turbidity in three lake classes.26 

Figure 8 . Acid neutralizing capacity for lakes of the U.S.27 

Figure 9. Dissolved oxygen for lakes of the U.S.28 

Figure 10. Schematic of a lakeshore.29 

Figure 11. Lakeshore habitat for lakes of the U.S. as percent of lakes 

in three condition classes.30 

Figure 12. Shallow water habitat for lakes of the U.S. as percent of lakes 

in three condition classes.30 

Figure 13. Physical habitat complexity for lakes of the U.S. as percent of lakes 

in three condition classes. 31 

Figure 14. Lakeshore disturbance for lakes of the U.S. as percent of lakes 

in three condition classes. 31 

Figure 15. Relative extent of poor stressors conditions. Relative risks of impact to 

plankton O/E and Attributable risk (combining Relative extent and Relative risk).32 

Figure 16. Percent of lakes, using three algal toxin indicators. 37 

Figure 17. Occurrence of microcystin in lakes.38 

Figure 18. Percentage predator fish with mercury and PCB levels above and below 

EPA recommended limits. 39 

Figure 19. Trophic state of lakes in the lower continental U.S. 45 

Figure 20. Ecoregions used as part of the National Lakes Assessment.48 

Figure 21. Biological condition (based on planktonic O/E taxa loss) across nine ecoregions.49 


vi 


National Lakes Assessment A Collaborative Survey of the Nations Lakes 






























Figure 22. Habitat condition of the nation's lakes across nine ecoregions based on lakeshore 

habitat.50 

Figure 23. Trophic state across nine ecoregions (based on chlorophyll-a,).51 

Figure 24. Comparison of exposure to cyanobacteria risk across nine ecoregions.51 

Figure 25. NLA results for the Northern Appalachians.53 

Figure 26. NLA results for the Southern Appalachians.55 

Figure 27. NLA findings for the Coastal Plains.57 

Figure 28. NLA findings for the Upper Midwest.59 

Figure 29. NLA findings for the Temperate Plains.61 

Figure 30. NLA findings for the Southern Plains.63 

Figure 31. NLA findings for the Northern Plains.65 

Figure 32. NLA findings for the Western Mountains.67 

Figure 33. NLA findings for the Xeric.69 

Figure 34. Proportion of NES lakes that exhibited improvement, degradation, or no change in 
phosphorus concentration based on the comparison of the 

1972 National Eutrophication Survey and the 2007 National Lakes Assessment.75 

Figure 35. Proportion of NES lakes that exhibited improvement, degradation, or no change in 
trophic state based on the comparison of the 1972 National Eutrophication 

Survey and the 2007 National Lakes Assessment.75 

Figure 36. Percentage and number of NES lakes estimated in each of four trophic classes 

in 1972 and in 2007 based on chlorophyll-a concentrations.76 

Figure 37. Change in percentage of chronically acidic lakes in the Adirondack Mountains 

and New England.77 

Figure 38. States with state-scale statistical surveys.85 

Figure 39. Comparison of lakes by trophic state for Vermont, the Northern Appalachians 

ecoregion, and the Nation, based on chlorophyll-a.87 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 





























| Executive Summary 



Photo courtesy of Frank Borsuk 


Executive Summary 

’V\ lake is the landscape's most 
beautiful and expressive feature. It 
is earth's eye; looking into which the 
beholder measures the depth of his 
own nature." 

These words by the American 
poet Henry David Thoreau underscore 
America's love of lakes. Lakes are 
places of reflection, relaxation, and 
repose, but like all our waters, they are 
being increasingly stressed. Growing 
anthropogenic pressures have prompted 
many governments, associations, and 
individuals to invest time in preserving or 
restoring the water quality of their lakes. 
To protect our nation's lakes, Americans 
must strive to understand how their 
actions as individuals and as a society are 
affecting them. 

Under the Clean Water Act (CWA), 
the U.S. Environmental Protection Agency 
(EPA) must report periodically on the 


condition of the nation's water resources 
by summarizing water quality information 
provided by the states. However, 
approaches to collecting and evaluating 
data vary from state to state, making it 
difficult to compare the information across 
states, on a nationwide basis, or over 
time. EPA and the states are continually 
working on ways to address this problem 
to improve water quality reporting. 

Congress, environmental groups, 
and concerned citizens routinely ask 
EPA questions about the quality of the 
nation's waters such asr What are the key 
problems in our waters? How widespread 
are the problems? Are there hotspots? 

Are we investing in water resource 
restoration and protection wisely? Are our 
waters getting cleaner? To better answer 
questions about the condition of waters 
across the country, EPA along with its 
state and tribal partners have embarked 
on a series of surveys to be conducted 
under the National Aquatic Resource 
Surveys (NARS) program. This relatively 


VIII 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 








Executive Summary 


new program provides statistically valid 
data and information vital to describing 
water resource quality conditions across 
the country, how these conditions vary 
with geographic setting, and the extent of 
human and natural influences. 

The National Lakes Assessment (NLA) 
is one in a series of annual NARS surveys. 
The NLA is the first statistical survey of 
the condition of our nation's lakes, ponds, 
and reservoirs. 1 Based on the sampling 
of over 1,000 lakes across the country, 
the survey results represent the state 
of nearly 50,000 natural and man-made 
lakes that are greater than 10 acres in 
area and over one meter deep. In the 
summer of 2007, lakes were sampled for 
their water quality, biological condition, 
habitat conditions, and recreational 


suitability. Field crews used the same 
methods at all lakes to ensure that results 
were nationally comparable. For many 
of the indicators, scientists analyzed the 
results against a reference condition. 
Reference conditions were derived from 
a set of lakes that were determined to be 
the least disturbed lakes for a region. 

Key Findings 

Biological Quality - 56% of the nation's 
lakes are in good biological condition. 
Natural lakes had a higher percentage of 
lakes in good condition than man-made 
lakes (Figure ES-1). 


National 
All Lakes 







49,546 


21.4% 



^22.3% 

■J 


Natural Lakes 
29,308 



Man-Made Lakes 
20,238 



| Good = <20% Taxa Loss Q Fair = 20% - 40% Taxa Loss | Poor = >40% Taxa Loss 


National Summary 
56% Good 
21% Fair 
22% Poor 



Figure ES-1. Biological condition of lakes nationally and based on lake origin. 


3 full report including technical supporting documents is available on-line at http://www.epa.qov/lakes_survey/ 


ix 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 































| Executive Summary 


Lake Physical Habitat - Of the stressors 
included in the NLA, poor lakeshore 
habitat is the biggest problem in the 
nation's lakes; over one-third exhibit poor 
shoreline habitat condition. Poor biological 
health is three times more likely in lakes 
with poor lakeshore habitat (Figure ES-2). 

Nutrients - About 20% of lakes in the 
U.S. have high levels of phosphorus or 
nitrogen. High nutrient levels are the 
second biggest problem in lakes. Lakes 
with excess nutrients are two-and-a half¬ 
times more likely to have poor biological 
health (Figure ES-2). 


Algal Toxins - The NLA conducted the 
first-ever national study of algal toxins in 
lakes. Microcystin - a toxin that can harm 
humans, pets, and wildlife - was found to 
be present in about one-third of lakes and 
at levels of concern in 1% of lakes. 

Fish Tissue Contaminants - A parallel 
study of toxins in lake fish tissue shows 
that mercury concentrations in game fish 
exceed health based limits in about half of 
lakes (49%); polychlorinated biphenyls 
(PCBs) at potential levels of concern are 
found in 17% of the lakes. 


Lakeshore Habitat 
Physical Habitat Complexity 

Shallow Water Habitat 
Total Nitrogen 

Total Phosphorus 
Lakeshore Disturbance 
Turbidity 
Dissolved Oxygen 

Percentage of Lakes Rated 
Poor for Each Stressor 


Extent of Stressor 


Number 
of Lakes 



35.9% 


32.4% 




20 . 1 % 


19.1% 


18.2% 


16.9% 


6.3% 


I 1.3% 


17.807 

16,033 

9,980 

9,467 

9,006 

8,364 

3,100 

632 


- 1 - 1 - 1 - 1 - 

0 20 40 60 80 100 


Relative Risk to 
Biological Condition 



--r-1-1- 

0 1 2 3 4 5 

Relative Risk 


Figure ES-2. Extent of stressor and relative risk of stressor to biological condition. 



National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 








































Executive Summary 


Trophic Condition - The NLA establishes 
the first nationally consistent baseline 
of trophic status. Over 36% of the 
nation's lakes are mesotrophic, based on 
chlorophyll-a concentrations. 

Changes in Trophic Condition - When 
compared to a subset of wastewater- 
impacted lakes sampled 35 years ago, 
trophic status improved in one-quarter 
(26%) and remained stable in over half 
(51%) of those lakes (Figure ES-3). This 
could indicate that, when considering 
rising populations in these areas, 
investments in wastewater pollution 
control are working. 


Implications 

As these results show, EPA and its 
state and tribal partners have begun 
to answer important national questions 
about the condition of the country's lakes. 
The results establish a national baseline 
status for future monitoring efforts which 
can be used to track scientifically credible 
trends in lake conditions. Successive 
surveys will help answer the question "Are 
our lakes getting better?" 




Change in Trophic State 

(Chlorophyll a) 



Figure ES-3. Proportion of National Eutrophication Survey 
(NES) lakes that exhibited improvement, degradation, or no 
change in trophic state based on the comparison of the 1972 
National Eutrophication Survey and the 2007 National Lakes 
Assessment. 


xi 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 















| Executive Summary 


For water resource managers, 
policymakers, boaters, swimmers, and 
others, the NLA findings suggest: 

• Poor lakeshore habitat condition 
imparts a significant stress on 
lakes and suggests the need for 
stronger management of shoreline 
development, especially as 
development pressures on lakes keep 
steadily growing. 

• Effective nutrient management 
continues to be needed in the nation's 
lakes. Excess levels of nutrients 
contribute to algae bloom, weed 
growth, reduced water clarity, and 
other lake problems. The adverse 
impact of nutrients on aquatic 

life, drinking water, and recreation 
remains a concern. 


• Local, state and national initiatives to 
protect the integrity of lakes should 
center on restoring the natural state 
of shoreline habitat - particularly 
vegetative cover and nutrient loading. 
Managers, residents, businesses, 
and community leaders should work 
together and enhance their efforts to 
preserve, protect, and restore their 
lakes and the natural environment 
surrounding them. 





National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 















CHAPTER I 


INTRODUCTION 



Pheips Lake, Grand Teton National Park, WY. Photo courtesy of Great Lakes Environmental Center. 


IN THIS CHAPTER 












!' 










► A Highly Valued and Valuable Resource 

► Why a National Survey? 

► The National Aquatic Resource Surveys 




















Introduction 


Chapter I 



Chapter 1 

Introduction 


A Highly Valued and 
Valuable Resource 

For anyone who went fishing as a child, 
water-skiing as a teen, or bird-watching as 
an adult, lakes are special places. Healthy 
lakes enhance the quality of life. In addition 
to supplying people with essential needs 
like drinking water, food, fiber, medicine, 
and energy, a lake's ecosystem is important 
in providing habitat for wildlife, recreation, 
aesthetics, reducing the frequency and 
severity of floods, shaping landscapes, and 
affecting local and regional climates. Lakes 
provide habitat for wildlife and enjoyment for 
people while supporting intrinsic ecological 
integrity for all living things. 

It is difficult to put a price on a natural 
treasure. Certainly, from a vacationer's 
perspective, lakes are invaluable, providing 
endless enjoyment and relaxation year- 
round. According to the U.S. Fish and Wildlife 
Service, 30 million Americans went fishing 
in 2006 and $42.2 billion was spent on 


recreational fishing. Locally, this translates 
into important economic and recreational 
benefits. For example, Lake Champlain, on 
the border of Vermont and New York, has 
over 65 beaches and 98 fishing-related 
businesses. According to the 2003 Lake 
Champlain Management Plan, in 1998 a total 
of $3.8 billion was generated from tourism. 

As more and more people use lakes for their 
livelihood and recreation, the competition for 
lake resources will continue. 

Protecting lake ecosystems is crucial 
not only to protecting this country's public 
and economic health, but also to preserving 
and restoring the natural environment for 
all aquatic and terrestrial living things. 

Lake protection and preservation can only 
be achieved by making informed lake 
management policy decisions at and across all 
jurisdictional levels. 

Why a National Survey? 

Water resource monitoring in the U.S. 
has been conducted by many different 
organizations over many decades using 
a variety of techniques. States and tribes 
conduct monitoring to support many Clean 
Water Act (CWA) programs. Section 305(b) 
of the CWA requires the U.S. Environmental 
Protection Agency (EPA) to report periodically 
on the condition of the nation's water 
resources by summarizing information 
provided by the states. Yet approaches to 
collecting and assessing data vary from 
state to state, making it difficult to compare 
the information across states or on a 
nationwide basis. Each of these monitoring 
efforts provides useful information relative 
to the goals of the individual programs, 
but integrating the data into a nationwide 
assessment has been difficult. 


2 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 









Introduction 


Chapter I 


In recent years, a number of independent 
reports have identified the need for improved 
water quality monitoring and analysis at a 
national scale. Among these, the General 
Accounting Office (2000) reported that 
EPA and states cannot make statistically 
valid assessments of water quality and 
lack the data to support key management 
decisions. The National Research Council 
(2001) recommended that EPA and states 
promote a uniform, consistent approach 
to water monitoring and data collection to 
better support core water management 
programs. The National Academy of Public 
Administration, in its 2002 report entitled, 
Understanding What States Need to Protect 
Water Quality , concluded that improved 
water quality monitoring is necessary to help 
state agencies make better decisions and 
use limited resources more effectively. These 
reports underscore the need for more efficient 
and cost-effective ways to understand the 
magnitude and extent of water quality 
problems, the causes of these problems, and 
practical ways to address the problems. 

The National Aquatic 
Resource Surveys 

To bridge this information gap, EPA, 
other federal agencies, states and tribes 
are collaborating to provide the public 
with improved environmental information. 
Statistical surveys are one way of addressing 
water resource assessment needs. By 
choosing a statistical design with standardized 
field and laboratory protocols, the EPA, states 
and tribes are able to collect and analyze 
data that are nationally consistent and 
representative of waterbodies throughout 
the U.S. These statistical surveys offer a 
cost-effective and scientifically valid way to 
fulfill statutory requirements, complement 
traditional monitoring programs, and support 
a broader range of management decisions. 


State Water Quality Reports 


Under section 305(b) of the Clean 
Water Act the states must submit 
biennial reports on the quality of their 
water resources. According to the 
most recently published National Water 
Quality Inventory Report (2004) the 
states assessed just over a third of the 
nation's waters — 37% or 14.8 million 
acres of the nation's 40.6 million acres 
of lakes, ponds and reservoirs. Of the 
lakes that were assessed, over half, 58% 
or 8.6 million acres, were identified as 
impaired or not supporting one or more 
of their designated uses such as fishing 
or swimming. The states cited nutrients, 
metals (such as mercury), sewage, 
sedimentation and nuisance species as 
the top causes of impairment. Leading 
known sources of impairment included 
agricultural activities and atmospheric 
deposition, although for many lakes, 
the sources of impairment remain 
unidentified. 


The surveys are designed to answer such 
questions as: 

• What is the extent of waters that 
support a healthy biological condition, 
recreation, and fish consumption? 

• How widespread are major stressors 
that impact water resource quality? 

• Are we investing in water resource 
restoration and protection wisely? 

• Are our waters getting cleaner? 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


3 














Introduction 


Chapter I 



The help of state partners was essential. 

Photo courtesy of Frank Borsuk. 


The specific goals of NARS are to generate 
scientifically valid information on the condition 
of water resources at national and ecoregional 
scales, establish baseline information for 
future trends assessment, and assist states 
and tribes in enhancing their water monitoring 
and assessment programs. 

The focus of NARS is on waterbodies 
as groups or populations, rather than as 
individual waters. For example, a state or 
local manager may be interested in nutrient 
levels in a given lake over time. NARS, on 
the other hand, allows one to examine the 
percentage of the nation's lakes that have 
experienced changes in nutrient levels over 
time. Findings such as these help drive 
national water quality management decisions. 

By generating population estimates of 
condition, the national statistical surveys 
and other statistical surveys have begun to 
provide answers to water resource questions 
with a known level of confidence. Working 
with its partners in states, tribes, territories, 
and other federal agencies, EPA has in recent 
years conducted statistical surveys of coastal 
waters, wadeable streams, and contaminants 
in lake fish tissue. The Agency's plans are 
to survey each of the five waterbody types, 


(lakes, rivers, streams, wetlands, and 
estuaries), on a 5-year rotating basis. EPA 
and its partners anticipate that the national 
surveys will continue to foster collaboration 
across jurisdictional boundaries, build state 
and tribal infrastructure and capacity for 
enhanced monitoring efforts, and achieve 
a robust set of statistically-sound data for 
better, more informed water resource quality 
management policies and decisions. 

The National Lakes Assessment (NLA) 
is one component of the National Aquatic 
Resource Surveys. This report summarizes 
the first-ever assessment of lakes across the 
continental United States using consistent 
protocols and a modern, scientifically- 
defensible statistical survey approach. 


Using the National Aquatic 
Resource Surveys 

Because of their scientific credibility, 
results from these surveys are being used 
in other scientific contexts. Most notably 
is the recent Heinz Center Report, The 
State of the Nation's Ecosystems, 2008. 
The Heinz Center's report is designed to 
provide a high level, comprehensive and 
scientifically sound account on the state 
of the nation's ecosystems. The Heinz 
Center uses data derived from EPA's 
Wadeable Streams Assessment report 
and National Coastal Condition Report to 
answer a number of outstanding questions 
about surface water health in our country. 
Information from on-going and upcoming 
national surveys will help fill gaps 
identified for other water resources and 
show trends in national water quality. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


















Think Globally — Act Locally. 
Restoring Mousam Lake 



"Every little bit helps" is perhaps the fundamental tenet 
of the estimated 3,000 to 4,000 local watershed groups 
across the country. Many communities are proving that 
they can make a noticeable difference in their neighborhood 
water resource. In York County, Maine, the Soil and Water 
Conservation District (SWCD) and the Mousam Lake Regional 
Association (MLRA) together with residents, townships, state 
agencies and others embarked on the Mousam Lake Water 
Quality Improvement Project. With widespread collaboration 
and some funding, they were able to clean up an impaired 
lake. 


Confronting Environmental Challenges 


Mousam Lake, a 863-acre lake located at the southern 
point of Maine, is a popular spot for boaters, anglers, and 
vacationers with its sandy shores and excellent cold and 
warm water trout fisheries. However, this 21- square mile 


watershed suffered from suburbanization and the conversion 


of forested land to driveways and parking lots. The lake's 
shoreline is heavily developed with over 700 seasonal and 


year-round homes and a heavily used boat ramp. For the past 


several decades, Mousam Lake has endured increased soil erosion and pollution from stormwater runoff 
from home construction, lawns and roads, and from failing septic systems. Higher levels of phosphorus 
have led to increased algal growth, decreased water clarity and lower levels of dissolved oxygen. In the 
2003 Total Maximum Daily Load (TMDL) assessment, excess phosphorus was identified as the major 
impairment. This downward trend in water quality resulted in a steady decline in the lake's once viable 
ecology and that of its surrounding aquatic habitats. Maine's Department of Environmental Protection 
(MDEP) attributes the problem to soil erosion and polluted runoff from residential properties and camp 
roads and effluent from inadequate septic systems located in the sandy soils around the lake. The TMDL 
assessment estimated that to meet Maine water quality standards, the annual amount of phosphorus 
reaching the lake would need to be reduced by 27%. 

A Decade of Effort 

Since 1997, the York County SWDC, MLRA, MDEP, and the towns of Acton and Shapleigh have 
been working together to address sources of pollution in Mousam Lake and foster long-term watershed 
stewardship. In 1999, the Mousam Lake Water Quality Improvement Project began. With help from EPA, 
the Maine Department of Transportation and the Maine Department of Agriculture negotiated cost share 
agreements with public and private landowners, and best management practices were initiated at 45 
priority sites. Technical assistance was provided to another 77 landowners. Projects included stabilizing 
shoreline erosion, improving gravel road surfaces and installing and/or upgrading roadside drainages. 
Twenty-one roads were repaired. In 2001, the Lake Youth Conservation Corps program was established 
to help with the implementation of best management practices, raise local awareness and commitment 



5 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


























to lake protection, and involve local youth in environmental stewardship. Since 2007, the youth have 
completed over 115 projects and continue to repair an average of 18 sites each year with annual 
support from the towns of Acton and Shapleigh. The total cost for the project was $1.1 million with local 
townspeople and others contributing over $400,000 in matching funds or in-kind services. 

A Cleaner, Healthier Lake 

In 1998 MDEP designated Mousam Lake as impaired and added it to the state's section 303(d) list of 
waters not meeting water quality standards, a requirement of the federal Clean Water Act. From 1999 
through 2006, a galvanized community tackled the problem and in 2007, monitoring results indicated that 
pollution loads in the lake were reduced by more than 150 tons/per year of sediment and 130 pounds/ 
per year of phosphorus. Water clarity depth has increased by a full meter from what it was ten years ago. 
Today, erosion control projects continue, thus keeping an estimated 76 tons of sediment and 64 pounds of 
phosphorus out of the lake each year. In 2006, Mousam Lake was removed from the state's 303(d) list of 
impaired waters. 

Staff and a small cadre of local leaders are continuing their campaign to keep the lake in good health. : 
Community outreach and education activities are ongoing to inform residents on how they can help. 

As part of the project, numerous newsletters have gone to every household in the watershed; MLRA 
holds annual meetings; the SWCD conducts workshops and delivers presentations; 30 construction sites 
have been acknowledged with "Gold Star" signs for environmental stewardship; and more than 200 
homeowners attended one of the thirteen "Septic Socials" to learn about septic system function, proper 
maintenance and water conservation. 

Every Little Bit Helps 

In many, many instances, small, local 
efforts can provide incentives and moral 
support for others. The success of the 
Mousam Lake project has inspired protection 
efforts on several neighboring lakes. The 
Acton Wakefield Watershed Alliance, the 
Square Pond Association, and the Loon Pond 
Association are now busy with their own 
restoration activities. For more information or 
tips from the people at Mousam Lake, contact 
Joe Anderson at York County SWCD at (207) 

324-0888, ianderson@vorkswcd.org or Wendy 
Garland (MDEP) at (207) 822-6320, wendv. 

Qarland@maine.QOv . 


f 



Vegetated buffer planting by Master Gardeners. 

Photo courtesy of Deborah Kendall. 




6 


National Lakes Assessment A Collaborative Survey of the Nation's Lakes 














CHAPTER 2 


DESIGN OF THE LAKES SURVEY 





IN THIS CHAPTER 

► Areas Covered by the Survey 

► Selecting Lakes 

► Lake Extent - Natural and Man-Made Lakes 

► Choosing Indicators 

► Field Sampling 

► Setting Expectations 


Photo courtesy of Washington Department of Ecology 























Chapter 2 


Design of the Lakes Survey 



Photo courtesy of Great Lakes Environmental Center 


Chapter 2 

Design of the Lakes Survey 

Lakes in the U.S. are as varied and 
unique as the landscape surrounding them. 
Receding glaciers formed thousands of lakes 
in the northwestern, upper midwestern, and 
northeastern parts of the country. Glacial 
action formed the Finger Lakes in New York, 
the Adirondack region, the kettle ponds in 
New England, as well as numerous lakes 
and "prairie potholes" located in Minnesota, 
Wisconsin, Iowa, and the Dakotas. In 
contrast, Oregon's Crater Lake is a water- 
filled volcanic depression, as is Yellowstone 
Lake in Wyoming. Lake Tahoe in California 
and Pyramid Lake in Nevada were formed 
by tectonic action. Along major rivers, like 
the Mississippi, oxbow lakes were formed 
from meandering river channels. Similarly, 
damming of the Columbia River and the 
Colorado River has created large man-made 
lakes and reservoirs. Smaller previously 
impounded streams comprise thousands of 
man-made lakes that provided energy for 
mills during industrialization. Natural lakes 
are scarce across the southern U.S. Many 
of the lakes in the arid southwestern and 
the humid southeastern U.S. are man-made 
lakes or reservoirs. The NLA survey included 
examples of all of these lake types. 


Areas Covered By 
the Survey 

The NLA encompasses the lakes, ponds 
and reservoirs of the continental U.S. 
including private, state, tribal and federal 
land. Although not included in this report, 
a lake-sampling project is underway in 
Alaska. Hawaii was not included in the 
national survey design. Information from the 
NLA is also presented for both natural and 
man-made lakes to present any difference 
in biological condition or responses to 
stressors. 

NLA results are reported for the 
continental U.S. and for 9 ecological regions 
(ecoregions). Areas are included in an 
ecoregion based on similar landform and 
climate characteristics (see Chapter 6 and 
Figure 20). Assessments were conducted 
at the ecoregion level because the patterns 
of response to stress are often best 
understood in a regional context. Some 
states participating in the NLA assessed 
lake condition at an even finer state-scale 
resolution than the ecoregional scale by 
sampling additional random sites within their 
state boundaries. Although these data are 
included in the analysis described in this 
report, state-scale results are not presented. 

Selecting Lakes 

Since a census of every lake in the 
country is cost prohibitive and beyond the 
reach of any program, EPA used a statistical 
sampling approach incorporating state-of- 
the-art survey design techniques. The first 
step, to ascertain the number of lakes in the 
country, was challenging because there is no 
comprehensive list or source for all lakes in 
the U.S. The best resource available is the 
USGS/EPA National Hydrography Dataset 
or NHD. The NHD is a multi-layered series 
of digital maps that reveal topography, 


8 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 








Chapter 2 


Design of the Lakes Survey 


Alaska's Lake Assessment 

By Terri Lomax, AK Department of Environmental Conservation 

The State of Alaska is about one-fifth the land mass of the continental U.S. Most of 
it is sparsely populated with extremely limited access. This limited access has helped 
preserve its rugged beauty and abundant natural resources. But Alaska is facing 
pressure from climate change and natural resource development. In the populated 
areas, the main causes of waterbody pollution are urban runoff and agricultural activity. 

There are an estimated 3 million lakes in Alaska. Instead of being a full participant in the National Lakes 
Survey, the State of Alaska opted to conduct a regional assessment. It focused on the Cook Inlet Basin, an 
area located in the southcentral part of the state; at 39,325 square miles, it is slightly smaller than the state 
of Kentucky. The State selected this area because the only agricultural activity of significance occurs within 
the Cook Inlet Basin. 

Alaska's lake assessment began in 2007 with a pilot study of four lakes. This pilot study was focused 
on access and coordinating logistics of sampling, procedures, and analysis. In 2008, the full project was 
completed with sampling of 50 lakes in the Cook Inlet ecoregion. The field crew was from the Alaska 
Department of Environmental Conservation and the University of Alaska Anchorage Environment & Natural 
Institute. In addition to the National Lakes Assessment indicators, fish tissue for metals and mercury, 
sediment trace metals, and core dating were added to the study. 

To date, all water chemistry, habitat, and lake profile data has been analyzed. Biological indicators, 
sediment metals and mercury, and fish tissue samples are currently being analyzed. All data collected must 
undergo quality assurance review before a final release of the data. However, initial results indicate that lakes 
in the Cook Inlet ecoregion of Alaska are healthy. 



area, flow, location, and other attributes of 
the nation's surface waters. When queried, 
NHD had 389,005 features listed that could 
potentially be lakes, ranging in size from less 
than 2.4 acres (1 hectare) up to the largest 
lakes in the country. Figure 1 illustrates the 
sample framework for the survey. 

Initial discussion by states and EPA 
regarding the scope of the survey focused on 
the size of lakes that were to be considered 
in the target population. It was agreed that, 
to be included, the site had to be a natural or 
man-made freshwater lake, pond or reservoir, 
greater than 10 acres (4 hectares), at least 
3.3 feet (1 meter) deep, and with a minimum 
of a quarter acre (0.1 hectare) open water. 
The Great Lakes and the Great Salt Lake 


were not included in the survey, nor were 
commercial treatment and/or disposal ponds, 
brackish lakes, or ephemeral lakes. After 
applying the criteria, 68,223 waterbodies 
were considered lakes by the NLA definition 
and thus comprised the target population 
(Figure 1, 3 rd bar). 

Other factors in lake selection included 
accessibility. In some cases, crews were 
either denied permission by the landowner or 
unable to reach the lake for safety reasons, 
such as sharp cliffs or unstable ridges. 

Using data from the crews' experience 
and pre-sampling reconnaissance, it was 
estimated that 27% or 18,677 lakes fell into 
the inaccessible category. This left 49,546 
lakes which could be assessed - inference 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 


9 









Chapter 2 


Design of the Lakes Survey 


National Hydrography Dataset (NHD) - 389,005 



Target Population - 68,223 


Excluded - less than 
4 hectares - 233,627 


Included -123,369 


Non-Target (not a lake) 
55,146 


Target - meets target 
population definitions - 68,223 


Target - not sampled 
18,677 


Target - Sampled - 49,546 


, 009 ^\- 


Excluded - other - 32 


NHD Sample Frame - 123,369 


Inference Population - 49,546 Lakes 


Figure 1. The process of lake selection. Starting with the NHD list 
of waterbodies, potential lakes are eliminated due to not meeting 
set criteria for inclusion in the survey (top bar), not being a lake 
(2nd bar), and inaccessibility (3rd bar) leaving the number of 
sampleable lakes or inference population (4th bar). 


population (bottom bar). In the end, a total 
of 1,028 lakes were sampled in the survey. 
These 1,028 lakes represent the population. 
For quality assurance purposes, 10%, of the 
target lakes were randomly selected for a 
second sampling later in the summer. 

Due to the selection process, the sampled 
NLA lakes represent 49,546 lakes or 73% 
of the target population. Thus, throughout 
this report, percentages reported for a given 
indicator are relative to the 49,546 lakes. For 
example, if the condition is described as poor 
for 10% of lakes nationally, this means that 
the number of lakes estimated to be poor for 
that indicator is 4,955 lakes. 

As an added feature, the design 
specifically included some sites from EPA's 
1972 National Lake Eutrophication Study 


(NES). By including this subset of lakes EPA 
hoped to be able to evaluate changes that 
occurred between the 1970s and 2007. 

In conjunction with the national survey, a 
number of states opted to sample additional 
lakes to achieve a state-wide probabilistic 
survey. EPA provided a list of additional lakes 
to the states so that any state wishing to 
conduct a state-scale statistical survey could 
do so. Sampling and processing methods from 
these additional lakes had to adhere to both 
the national field and laboratory protocols. 
Eight states (MI, WI, IN, MN, TX, OK, ID, 
and WA) took advantage of the opportunity 
and the results from the additional sites were 
analyzed along with the national data. Some 
states increased the number of sites, but only 
collected a subset of indicators. Still other 
states opted to expand the list of indicators 
to address issues specific to their state; for 
example, Minnesota used its state-scale 
survey to assess pesticides. 

Figure 2 shows the location of the lakes 
that were sampled for the NLA. The surveyed 
lakes cover an area of 3.8 million acres of 
surface water spread across the national 
landscape. 

The site selection for the survey ensures 
that EPA can make unbiased estimates 
concerning the health of the target population 
of lakes with statistical confidence. The 
greater the number of sites sampled, the 
more confidence in the results. The number 
of sites included in the survey allows EPA to 
determine the percentage of lakes nationwide 
and within predetermined ecoregions that 
exceed a threshold of concern with 95% 
confidence. In the graphs throughout this 
report, the margin of error is provided as thin 
lines on either side of the bars and represent 
the 95% confidence interval for the estimate. 


10 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 











Chapter 2 


Design of the Lakes Survey 



jnada 


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-7 


• v f* 4* t r v 

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Lake Typ« 

• Natural 

• Man-made 



Atlantic 

Ocetat 


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N 

s 

NLA Sampled Sites 

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CtnMMHMMnc-W 
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Figure 2. Location of lakes sampled in the NLA. Natural lakes are the blue dots; Man-made lakes are brown. 


For national estimates, the margin of error 
around the NLA findings is approximately 
±5% and for ecoregions the margin of error 
is approximately ±15%. For example, for the 
national biological condition findings, the NLA 
estimates that 22.4% of the nation's lakes 
are in poor condition and that the margin of 
error is +/- 4%. This means that there is a 
95% certainty that the true value is between 
18.4% and 26.4%. 

Lake Extent - 

Natural and Man-made Lakes 

NLA analysts, comprised of lake science 
experts both within and outside the Agency, 
examined available records for each sampled 
lake to determine its origin. They considered 
natural lakes as those that existed pre- 


European settlement, even if presently 
augmented by means of an impoundment 
or other earthworks. Using this operational 
definition, 41% of the estimated 49,546 lakes 
are man-made reservoirs, while 59% are of 
natural origin. This means that nearly one- 
half of today's lakes were not here when the 
colonists arrived. 

While natural lakes come in many different 
sizes, most man-made lakes are relatively 
small. A total of 52% of man-made lakes are 
10-25 acres (4-10 hectares) in size compared 
with only 34% of the natural lakes in that 
small lake size category. Large lakes, over 
12,500 acres (5,000 hectares), are rare in the 
U.S., comprising only 0.3% of natural lakes 
and 0.6% of man-made lakes (Figure 3). 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 


II 











































Chapter 2 


Design of the Lakes Survey 



0 20 40 60 80 100 

Percentage of Lakes 


Figure 3. Size distribution of lakes in the U.S. overall and for natural 
and man-made lakes. 

Choosing Indicators 

Scientists and lake managers recognize 
that lake ecosystems are dynamic and 
indicators selected to characterize lakes 
must represent important aspects of water 
resource quality. For the NLA, a suite of 
chemical, physical and biological indicators 
were chosen to assess biological integrity, 
trophic state, recreational suitability, and key 
stressors impacting the biological quality of 
lakes. 


Although there are many more indicators 
and/or stressors that affect lakes, NLA 
analysts believe these to be among the 
most representative at a national scale. The 
NLA survey marks the first time all these 
indicators have been applied consistently and 
simultaneously to lakes on a national scale. 

For this assessment, NLA analysts looked 
at data of phytoplankton, zooplankton and 
sediment diatoms in an effort to characterize 
the biological condition of lakes. It was 
during the analysis that it was decided 
that the results of the phytoplankton and 
zooplankton assessment would serve as 
the primary biological indicator. To address 
recreational/human health related concerns, 
the NLA looked at actual levels of the algal 
toxin microcystin, along with cyanobacterial 
cell counts and chlorophyll-a concentrations 
as indicators of the potential for the 
presence of algal toxins. The presence and 
concentration of microcystin were used 
as the primary indicators for recreational 
condition. Chlorophyll-a was used as the 
primary indicator of trophic status. Although 
fish samples were not collected in the survey, 
NLA analysts also looked at the findings of a 
parallel study of contaminants in fish tissue. 

Both physical and chemical stressor 
indicators were measured. For example, 
shorelines affect biological communities 
in many ways, such as providing food and 


Biological 

Recreational 

Chemical 

Physical 

• Sediment diatoms 

• Phytoplankton (algae) 

• Zooplankton 

• Benthic 

macroinvertebrates* 

• Algal density 
(chlorophyll-a) 

• Invasive species* 

• Pathogens * (enterococci) 

• Algal toxin (microcystins) 

• Algal cell counts 
(Cyanobacteria) 

• Algal density 
(chlorophyll-a) 

• Nutrients 

(phosphorus & nitrogen) 

• Water column profile 
(dissolved oxygen, 
temperature, pH, 
turbidity, acid neutralizing 
capacity, salinity) 

• Sediment mercury* 

• Lakeshore habitat 
cover and structure 

• Shallow water habitat 
cover and structure 

• Lakeshore human 
disturbance 


* These indicators are still under evaluation and are not included in this report. Results will be published at a later date. 


: 

National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 
































Chapter 2 


Design of the Lakes Survey 


shelter for aquatic wildlife, and by moderating 
the magnitude, timing, and pathways 
of water, sediment, and nutrient inputs. 
Shorelines also buffer the lake from human 
activities. Water quality characteristics, such 
as nutrient levels and dissolved oxygen, 
create environments essential for aquatic 
organisms to survive and grow. At the 
bottom of the lake, sediment diatoms, a type 
of algae that live on the bottom and leave 
fossil remains, allow examination of current 
water quality conditions, such as phosphorus 
levels, along with historical conditions. These 
indicators of stress were selected because 
water quality stressors impact the biological 
health of lakes- from primary producers 
(phytoplankton or algae) to small openwater 
animals (zooplankton) to macroinvertebrates 
(insects, mollusks and crustaceans) and fish. 


Launching a field survey boat in Kansas. 

Photo courtesy of Ben Potter. 



Lake Habitats 



Lakes are highly interactive systems. The physical and chemical make-up of a lake supports a specialized 
community of biological organisms unique to the surrounding environment. Lakes and ponds are still- 
water habitats that host a large array of floating organisms that cannot survive in flowing water. For many 
organisms, shoreline and shallow water habitats provide refuge from predation, living and egg-laying 
substrates, and food. In addition to aquatic inhabitants, a wide number of terrestrial animals rely on lakes for 
their food. For example, in a typical summer, a moose can eat over 17V2 lbs of aquatic plants per day. A 3V2 lb 
adult osprey can consume some 270 lbs offish in one year 

The indicators include both the vegetation and physical features along shorelines and adjacent upland areas. 
Shoreline structure affects nutrient cycling, biological production, and even sedimentation rates within the 
lake. The zone of transition between the lakeshore and the water's edge is an area where considerable 
biological interactions occur and is critically important to benthic communities, fish, and other aquatic 
organisms. The relationship between the terrestrial and aquatic environments is characterized by the 
movement of nutrients/food from the shore to the water (e.g., fish making use of emergent plants for food or 
shelter), and the reverse movement from the water back to the shore (e.g., seasonal flooding of shorelines, 
shore birds feeding on aquatic insects and crustaceans). 

Human activities along lakeshores often adversely affect ecosystem functions by lessening the amount and 
type of optimal habitat available. Habitat cover or protection, in the form of woody snags, overhanging trees, 
and aquatic plants, becomes markedly reduced. A poor habitat cover adversely impacts aquatic plants, 
fish, and other living things in and around the lake. Alterations of these and other types of habitat features 
can affect biological integrity even in lakes where the water is not polluted. Therefore, the physical habitat 
condition of the land-water interface is critically important to overall lake condition. 


v ' | 13 

National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 















Chapter 2 


Design of the Lakes Survey 


Field Sampling 

In preparation for the survey, each target 
lake was screened to verify that it met the 
established criteria for inclusion in the survey. 
Throughout the summer of 2007, 86 field 
crews, consisting of 2 to 4 people each, 
sampled lakes from Maine to California. To 
ensure consistency in data collection and 
quality assurance, the crews attended a 
three-day training session, used standardized 
field methods and data forms, and followed 
strict quality control protocols including field 
audits. 

At each lake site, crews collected samples 
at a single station located at the deepest 
point in the lake and at ten stations around 
the lake perimeter (Figure 4). At the mid¬ 
lake station, depth profiles for temperature, 
pH, and dissolved oxygen were taken with 
a calibrated water quality probe meter or 


multi-probe sonde. A Secchi disk was used 
to measure water clarity and depth at which 
light penetrates the lake (the euphotic 
zone). NLA analysts used these vertical 
profile measurements to determine the 
extent of stratification and the availability 
of the appropriate temperature regime 
and level of available oxygen necessary 
to support aquatic life. Single grab water 
samples were collected to measure nutrients, 
chlorophyll-a, phytoplankton, and the algal 
toxin microcystin. Zooplankton samples were 
collected using a fine mesh (80pm) and 
course mesh (243pm) conical plankton net. 

A sediment core was taken to provide data 
on sediment diatoms and mercury levels. The 
top and bottom layers of the sediment core 
were analyzed to detect possible changes in 
diatom assemblages over a period of time. 



Profunda / 


Uttoral 


Observation station 
positioned 10 m 
offshore for sampling 


Stations equidistant 


Water chemistry 

Multiprobe 

Phytoplankton 

Zooplankton 

Sediment core 

Microcystin 


•Pathogen 
sample collected 
at last physical 
habitat site 


Physical habitat and benthic 
sampling stations (A-J) - 
Starting point randomly 
selected o priori 


Riparian I Vlim 
zone 


Shoreline 
zooe (1 m) 


Benthic sample collected 

from dominant littoral habitat within 

Each physical habitat station 


Observation station 


Figure 4. NLA sampling approach for a typical lake. Sampling locations are denoted by letters A-J and Z. Riparian, 
littoral, sublittoral, and profundal lake zones are depicted, as is the schematic design of a shoreline physical habitat 
station. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 












Chapter 2 


Design of the Lakes Survey 


Along the perimeter of the lake, crews 
collected data and information on the physical 
characteristics that affect habitat suitability. 
Information on substrate composition was 
recorded along the ten pre-determined 
stations. Benthic macroinvertebrates, 
collected with a 500pm D-frame net, and 
water samples for pathogen analysis were 
collected at the first and last station, 
respectively. Filtering and other sample 
preparations took place back on shore. 
Sampling each lake took a full day and many 
crews spent weeks in the field. At the end of 
the season, field crews collected 8,536 water 
and sediment samples; took over 5,800 direct 
measurements; and recorded in excess of 
620,000 observations. 

Setting Expectations 

Two types of assessment thresholds were 
used in the NLA. The first is fixed thresholds. 
Fixed thresholds are based on longstanding 
accepted values from the peer reviewed 
scientific literature. They are well established, 
and widely and consistently used. An example 
of this is standard chlorophyll-a thresholds 
which are used to classify lakes into the 
different trophic categories. 

The second type of threshold is based on 
the distribution (/'.e., the range of values) of a 
particular indicator derived from the reference 
lakes data. 

Selecting Reference Lakes 

In order to assess the condition of the 
country's lakes, results were compared to 
conditions in a suite of "reference lakes." A 
reference lake in the NLA is a lake (either 
natural or man-made) with attributes (such as 
biological or water quality) that come as close 
as practical to those expected in a natural 
state, i.e. r least-disturbed lake environment. 
NLA analysts used the reference distribution 


as a benchmark for setting thresholds for 
good, fair, and poor condition for each of the 
indicators. 

EPA's experience with past surveys 
showed that only a small portion of the 
sampled population of lakes will be of 
reference quality. EPA used both identified 
lakes that were thought to be of high quality 
as well as high quality lakes from the random 
site selection process to serve as candidate 
reference lakes that might ultimately serve 
as "least-disturbed" benchmark reference 
sites. The candidate lakes were sampled 
identically to, and in addition to the target 
lakes. Subsequently, data results from all 
sampled lakes were evaluated against the 
reference screening criteria to determine 
the final set of lakes that would be used to 
characterize the reference condition. NLA 
analysts used a number of independent 
variables reflecting human influence as 
classification and screening criteria, e.g., 
limnological shoreline index, chloride content, 
total water column calcium, and others. Two 
parallel groups of reference lakes were set, 
one for biological condition, and another for 



Retrieving a sediment core. 

Photo courtesy of Great Lakes Environmental Center. 


National Lakes Assessment: A Collaborative Survey of the Nations Lakes 







Thresholds - Good, Fair, and Poor 


Chapter 2 


Design of the Lakes Survey 


nutrient stressors. The latter set of reference 
sites was developed so that nutrient levels 
could be used in screening reference lakes for 
biological condition. 

When considering reference condition, it 
is important to remember that many areas 
in the United States have been altered - with 
natural landscapes transformed by cities, 
suburban sprawl, agricultural development, 
and resource extraction. To reflect the 
variability across the American landscape, 
these least-disturbed lakes diverge from 
the natural state by varying degrees. For 
example, highly remote lakes like those in the 
upper elevation wilderness areas of Montana 
may not have changed in centuries and are 
virtually pristine, while the highest quality, 
least-disturbed lakes in other parts of the 
country, especially in urban or agricultural 
areas, may exhibit different levels of human 
disturbance. The least-disturbed reference 
sites in these widely influenced watersheds 
display more variability in quality than those 
in watersheds with little human disturbance. 
Thus in reference conditions across the 
country, i.e., the "bar" for expectations may 
be different. The resulting reference lakes 
represent the survey team's best effort at 
selecting lakes that are the least disturbed 
nationally and in specific regions across the 
country. 


After the reference lakes were selected 
and reference condition was determined, 
thresholds against which the target lakes are 
compared were set. For NLA, each indicator 
for a lake was classified as either "good," 
"fair," or "poor" relative to the conditions 
found in reference lakes. That is, "good" 
denotes an indicator value similar to that 
found in reference lakes, "poor" denotes 
conditions definitely different from reference 
conditions, and "fair" indicates conditions 
on the borderline of reference conditions. 
Specifically, these thresholds are then applied 
to the results from the target lakes and are 
classified as follows: lake results above 25% 
of the reference range values are considered 
"good;" below the 5% of the reference range 
value are "poor;" and those between the 
5% and 25% are "fair" (Figure 5). These 
"good," "fair," "poor" designations however 
are not intended to be a replacement for the 
evaluation by states and tribes of the quality 
of lakes relative to specific water quality 
standards. 


25% of reference distribution 



Figure 5. Reference condition thresholds used for good, fair, and poor assessment. 


16 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 



















HIGHLIGHT 



Surveying the Nation’s Lakes for 
Invasive Aquatic Species 


Amy P. Smagula 

New Hampshire Department of Environmental Services 


On every continent, in nearly all aquatic habitat types, at all levels of the food web, invasive species 
have made an impact. Invasive aquatic species can be described as those species that live in water but are 
generally not native to a particular waterbody. In general they have traits or characteristics that suggest a 
competitive ecological advantage over native species. Invasive species grow rapidly and/or aggressively, 
so that they can eventually dominate a habitat to the detriment of native creatures that already live there. 
Invasive aquatic species include a whole range of organisms, including plants, animals, pathogens, and 
others. 

The types of invasive aquatic species in our lakes are 
numerous and diverse, and can include aquatic plants that 
either root in substrate (like Eurasian watermilfoil or Hydrilla) 
or that float on the surface of the water (like the giant salvinia). 
They include larger animals such as fish (like the snakehead 
fish), and macroinvertebrates (like the zebra mussel). They also 
include those seen only with the aid of a microscope, such as 
filamentous algae or the spiny water flea. 

The pathways for invasive aquatic species introductions 
are varied, and include ballast water discharges from large 
vessels, retail industries like the aquarium and home water 
garden trades, and even internet suppliers of aquatic species. 
Once a species becomes established in a waterbody, either 
by accidental (e.g., contaminated boat) or intentional means 
(e.g., dumping of an aquarium or direct planting), it is transient 
recreational equipment (motor boats, kayaks, diving gear, etc.) 
that causes the lake-to-lake spread of these species. 

Depending on the point of introduction and transport 
pathways, species can become widely distributed or remain 
as localized infestations. Unfortunately, many invasive aquatic 
species are highly adaptive, and can survive and thrive in a 
wide range of environmental conditions. Big or small, plant 
or animal, invasive aquatic species in our lakes can have 
detrimental effects on the very attributes of those waterbodies 
that scientists, citizens, and environmental stewards are trying 
to evaluate and preserve. 

How Can Data from the NLA Survey Help? 

One of the goals of the National Lakes Assessment (NLA) is to provide citizens and governments with 
current information on the health of our lakes so that they can take action to prevent further degradation. 
Data on invasive aquatic species can be used to help determine which of these species has been 


Invasive Aquatic Species: 


Grow very quickly and spread rapidly 
to occupy large areas; 

Have various strategies for 
reproduction; 

Survive in a range of conditions; 

' Have no natural predators to 
control them; 

1 Take over areas from native 
plants/animals and can thus 
be ecologically devastating; 

Pose serious economic problems 
in terms of control costs and costs 
attributable to habitat loss and 
recreational impairments to 
waterbodies, including reductions 
in property values on infested 
waterbodies; 

Are very difficult if not impossible 
to control; and 

Threaten nearly half of the species 
listed under the Endangered 
Species Act. 



National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 

















documented in a state or region, and if those are well established populations or if they are pioneering 
and can be eliminated or halted before other waterbodies in the area are affected. These data may also 
be used to assist with risk assessments for an area, based on what has been found in neighboring states, 
coupled with tourism and recreational data for that region. 

The Key is Prevention, Early Detection, & Rapid Response 

Preventing the introduction of invasive aquatic species is paramount to protecting a waterbody. Many 
states and regional working groups have established education campaigns to alert lake users and others 
about the threats posed by invasive aquatic species and to hopefully prevent a new infestation by proper 
care of transient recreational vessels and gear. Additionally, many states have developed prohibited 
species lists in an effort to prevent overland transport and sale of these invasive species. 

When prevention fails and an infestation does occur, early detection is critical. Individual lake 
associations, special interest groups, and homeowners are encouraged to look for new infestations on a 
regular basis during the growing season, particularly if they live on a waterbody that receives a high level 
of use by transient boaters. A small new infestation is much more easily contained or eradicated than a 
dense and large-scale infestation. A network of volunteer monitors around a waterbody can look for signs 
of invasive species and report to key officials who can effectively deal with a potentially new infestation. 

State officials should be knowledgeable and poised for a rapid response to contain and control an 
infestation. They should be aware of appropriate management actions for the species in question and how 
to best approach the problem. Fortunately, many states have developed specific plans for aquatic nuisance 
species management, so that an immediate response can be made. 


Hydrilla 

( Hydrilla verticil la ta ) 

First Identified in US: 1960 

Native Range: Africa 

U.S. Distribution: Widespread throughout the east and 
southeast, CA as well as occurrence in other states in the U.S. 

Description: Narrow leaves whorled around the 20 ft main 

stem. It is the most invasive submergent plant in the U.S., and 1 

can even out-compete invasive watermilfoil by canopying over 

the surface. It has been observed to grow up to a half-inch per 3t /v—T tj) 

day in optimum conditions. 

Impacts: This plant forms thick impenetrable growth in the y* ' ' 

water column of lakes. It can impact native aquatic plants and 
animals and cause problems for recreation and navigation on 
waterbodies that it infests. 


First Identified in US: 1988 

Zebra mussel 

(Dreissena polymorpha) 

INdtlVG Kdliy 6* tUt dSId 

U.S. Distribution: All of the Great Lakes and many £9gn 

associated tributaries, plus other states throughout the U.S. 

Description: Sticky strands secreted from one side of shell. MM 

Can grow very thick on surfaces. \|f vH 

Impacts: Documented to grow very thick on surfaces, foul 

marine engines, clog intake pipes, wash up in windrows on 

beaches, and alter the aquatic food web by reducing the IWP 


amount of algae in the water due to high filter-feeding rates. 

Photos credits: Hydrilla, Amy P. Smagula, NH DES. Zebra mussels, NH SeaGrant. 


18 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 












CHAPTER 3 


THE BIOLOGICAL CONDITION 
OF THE NATION'S LAKES 



IN 

► 

► 

► 


THIS CHAPTER 

Lake Health - The Biological Condition of Lakes 
Stressors to Lake Biota 
Ranking of Stressors 






Chapter 3 


The Biological Condition of the Nation’s Lakes 



Photo courtesy of Great Lakes Environmental Center 


Chapter 3 

The Biological Condition 
of the Nation's Lakes 

The Clean Water Act explicitly aims "to 
restore and maintain the chemical, physical 
and biological integrity of the nation's waters." 
Although the NLA report does not include 
all aspects of biological integrity or review 
all possible chemical, physical or biological 
stressors known to affect water quality, it 
does present the findings of some important 
indicators for estimating the condition of the 
nation's lakes and characterizing the key 
influences. 

This and the following two chapters 
describe the results of the NLA using three 
approaches to assess lake condition. The 
first approach evaluates whether lakes are 
able to support healthy aquatic plant and 
animal communities. Analysts evaluated key 
stressors to lake biota, such as chemical 


and physical habitat attributes, and ranked 
the stressors in order of importance. In 
the second approach, the recreational 
suitability of lakes was assessed and the risk 
of exposure to algal toxins was evaluated 
(Chapter 4). The third approach was to 
evaluate trophic state based on chlorophyll-a 
levels (Chapter 5). 

Lake Health - 

The Biological Condition of Lakes 

The biology of a lake is characterized in 
terms of the presence, number, and diversity 
offish, insects, algae, plants and other 
organisms that together provide accurate 
information about the health and productivity 
of the lake ecosystem. The number and kinds 
of plant and animal species present in a 
lake system are a direct measure of a lake's 
overall well-being. 

The biological condition assessment is 
based on information from two biological 
communities or assemblages - phytoplankton 
and zooplankton. The primary basis for 
assessing biological health is an index of taxa 
loss which is applied to the phytoplankton and 
zooplankton data. The NLA uses a measure 
of planktonic taxa loss as the predominant 
measure of overall lake condition because it is 
based on both plant and animal data and thus 
will reflect a broader perspective of trends in 
lakes. A second method to assess biological 
health uses an index of biotic integrity that 
is applied to sediment diatoms, a distinct 
type of phytoplankton. Both models use the 
biological reference conditions developed from 
the set of reference lakes. 

Biological Indicators 

Phytoplankton. Phytoplankton are micro¬ 
scopic plants (algae) that float in the water 
and are usually responsible for both the color 


20 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 








Chapter 3 


The Biological Condition of the Nation’s Lakes 


and clarity of lakes. Because of their ability 
to photosynthesize (/.e., they use the sun's 
energy to turn carbon dioxide and water into 
food and energy), they are a primary source 
of energy in most lake systems, providing the 
food source for higher order organisms such 
as zooplankton or small fishes. Phytoplankton 
are remarkably diverse. For example, cer¬ 
tain phytoplankton can regulate the depth at 
which they reside, optimizing their ability to 
access both nutrients and light. Others are 
specific to certain habitats within lakes, and 
to certain nutrient and chemical conditions. 

Zooplankton. Zooplankton are small free- 
floating aquatic animals. The zooplankton 
community constitutes an important 
element of the aquatic food chain. These 
organisms serve as an intermediary species 
in the food chain, transferring energy from 
planktonic algae (primary producers) to 
larger invertebrate predators and fish. Both 
phytoplankton and zooplankton are highly 
sensitive to changes in the lake ecosystem. 
The effects of environmental disturbances 
can be detected through changes in species 
composition, abundance, and body size 
distribution of these organisms. 



Centrate (left) and pinnate (right) diatoms. 

Image courtesy of J. Smol as provided by D. Charles 


Diatoms. Diatoms are a group of algae. 
Typically abundant in marine and freshwater 
habitats, diatoms account for at least 20% of 
the primary production of energy on earth. 
Unique among the algae, diatoms have 
cell walls composed of silica (glass), which 
are intricate and beautiful as well as useful 



Collecting a zooplankton sample in Texas. 

Photo courtesy of Texas Commission of Environmental Quality. 


for identifying individual species. In lakes, 
diatoms grow suspended in water as well as 
attached to substrates. Biologists use the 
diatoms in the water column and those on the 
lake bottom as a reflection of conditions in 
the lake. When diatoms die, they settle to the 
bottom and their silica shells remain intact. 
Over time their silica shells are preserved in 
layer upon layer of lake sediments enabling 
researchers to look at conditions that existed 
in the past. Similar to other biological 
indicators, diatoms integrate the physical 
and chemical conditions of the lake and 
surrounding watershed in which they reside. 
The environmental conditions under which 
particular diatom species flourish vary greatly 
and have been well described, making them a 
useful indicator. 

Index of Taxa Loss - 

The Observed/Expected (O/E) Ratio 

NLA analysts used the planktonic O/E 
taxa loss model to assess the condition of 
the planktonic community, combining data 
from both phytoplankton and zooplankton. 
The O/E measure looks at whether or not 
organisms (taxa) one would expect to find, 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


21 






















Chapter 3 


The Biological Condition of the Nation’s Lakes 


based on reference lakes, are in fact present. 
The model allows a precise matching of the 
taxa found in the sample — in this case 
phytoplankton and zooplankton taxa — with 
those that should occur under the specified 
natural environmental conditions defined 
by the reference sites. The list of expected 
taxa (or"E") at individual sites are predicted 
from a model developed from data collected 
at reference sites. By comparing the list 
of taxa observed (or "O") at a site with 
those expected to occur, one can quantify 
the proportion of taxa that have been lost 
presumably due to stressors present in 
the lake. The O/E model is widely used 
nationally and internationally to assess the 
condition of aquatic communities. The index 
is particularly attractive because it allows a 
direct comparison of conditions across the 
different types of aquatic systems (e.g., 
lakes, wetlands, streams, and estuaries) 
that will be assessed by the national aquatic 
resource surveys. 




Measuring physical habitat data with flooded terrestrial 
vegetation. Photo courtesy of Dave Mercer. 


Typically O/E values are interpreted 
as the percentage of the expected taxa 
present. Each tenth of a point less than 1 
represents a 10% loss of taxa at the site; 
thus, an O/E score of 0.9 indicates that 90% 
of the expected taxa are present and 10% 
are missing. The higher the percentage, the 
healthier the lake. As with all indicators, 

O/E values must be interpreted in context 
of the quality of reference sites because the 
quality of reference sites available in a region 
sets the bar for what taxa may be expected. 
Regions with lower-quality reference sites 
may have fewer taxa or different taxa and 
thus will have a lower bar. Although an O/E 
value of 0.8 means the same thing regardless 
of a region, i.e., 20% of taxa have been 
lost relative to reference conditions in each 
region, the true amount of taxa loss will be 
under-estimated if reference sites are of 
lower quality, meaning more disturbed than 
reference sites in comparable regions. 

For the phytoplankton and zooplankton 
data, NLA analysts developed regionally- 
specific O/E models to predict the extent of 
taxa loss across lakes of the United States. 
They defined three categories of plankton 
taxa loss: good (<20% taxa loss), fair (20- 
40% taxa loss), and poor (>40% taxa loss). 

Index of Biological Integrity - 
The Lake Diatom Condition Index 

The Lake Diatom Condition Index 
(LDCI) — or the Diatom IBI — is similar in 
concept to an economic indicator (e.g., the 
Consumer Confidence Index) in that the 
total index score is the sum of scores for a 
variety of individual measures. To calculate 
economic indicators, economists look at a 
number of metrics, including new orders for 
consumer goods, building permits, money 
supply, and others that reflect economic 
growth. To determine the LDCI, ecologists 


22 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 










Chapter 3 


The Biological Condition of the Nation’s Lakes 


looked at taxonomic richness, habit and 
trophic composition, sensitivity to human 
disturbance, and other aspects of the 
assemblage that are reflective of a natural 
state. For the LDCI, NLA analysts calculated 
regionally-specific thresholds that were based 
on percentages of reference lake distributions 
of LDCI values. 2 

The development of the LDCI is a 
groundbreaking addition to the tools available 
to perform lake assessments. The metrics 
used to develop the LDCI for the NLA covered 
five characteristics of diatom assemblages 
that are routinely used to evaluate biological 
condition: 

Taxonomic richness: This characteristic 
represents the number of distinct taxa, or 
groups of organisms, identified within a 
sample. A greater number of different kinds 
of taxa, particularly those that belong to 
pollution-sensitive groups, indicate a variety 
of physical habitats and an environment 
exposed to generally lower levels of stress. 

Taxonomic composition: Ecologists 
calculate composition metrics by identifying 
the different taxa groups, determining which 
taxa in the sample are ecologically important, 
and comparing the relative abundance of 
organisms in those taxa to the whole sample. 
Healthy (good quality) lake systems have 
diatoms from across a larger number of taxa 
groups, whereas stressed (poor quality) lakes 
are often dominated by a high abundance of 
organisms in a small number of taxa that are 
tolerant of pollution. 

Taxonomic diversity: Diversity metrics 
look at all the taxa groups and the distribution 
of organisms among those groups. Healthy 
lakes should have a high level of diversity of 
diatoms present. 



Subsampling zooplankton samples. 

Photo courtesy of EcoAnalysts. 


Morphology: Organisms are characterized 
by certain adaptations, including how they 
move and where they live. These habits 
are captured in morphological metrics. For 
example, some are designed to move freely 
up and down within the water column to 
maximize nutrient uptake or light exposure, 
while others may develop adaptations, such 
as coloration, to avoid predation. A diversity 
of such attributes is reflective of a lake 
that naturally includes a diversity of habitat 
niches. 

Pollution tolerance: Each taxa can tolerate 
a specific range of chemical contamination, 
which is referred to as their pollution 
tolerance. Once this range is exceeded, the 
taxa are no longer present. Highly sensitive 
taxa, or those with a low pollution tolerance, 
are found only in lakes with good water 
quality. 


2 The numerical threshold for the diatom index and many of the other NLA indicators can be found in the Technical Appendix. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


23 














Chapter 3 


The Biological Condition of the Nation’s Lakes 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 


_.. . . . _ Number , Number 

Planktonic O/E otLaxes Diatom IBI ofLakes 



0 20 40 60 80 100 

Percentage of Lakes 

I 1 < 20% = Good 
20 - 40% = Fair 
> 40% = Poor 


0 20 40 60 80 100 

Percentage of Lakes 

I I Fair 
I I Poor 


Figure 6. Assessment of quality using the Planktonic O/E Taxa Loss and Lake Diatom Condition Index. * 3 


Findings of the Biological Assessments 

Using the planktonic O/E, or taxa loss 
model, 56% of the nation's lakes are in good 
condition, while 21% are in fair condition, 
and 22% are in poor condition (Figure 6). The 
LDCI shows similar results with 47% of lakes 
in good condition, 27% in fair condition, and 
23% in poor condition. For the continental 
U.S., this means about half of the country's 
lakes are in good condition, while the other 
half are experiencing some level of stress that 
is negatively affecting the aquatic biological 
communities. 

Natural lakes in general exhibit slightly 
lower overall plankton taxa loss than man¬ 
made lakes. Sixty-seven percent of natural 


lakes are in good condition as compared 
to 40% of man-made lakes - a statistical 
difference. The LDCI, on the other hand, 
indicates that the proportion of lakes 
exhibiting good conditions does not vary 
significantly between natural and man-made 
lakes. However, 30% of natural lakes as 
compared to 13% of man-made lakes exhibit 
poor biological condition based on the diatom 
LDCI. 

Although in many cases the results of 
the planktonic O/E analysis are similar to 
the results of the diatom LDCI analysis, 
such agreement will not always occur. The 
taxa loss index examines a specific aspect 
of biological condition (biodiversity loss) 
and the index of biological integrity analysis 


j 

3 For this and all figures in this report, values for good, fair and poor may not add to one hundred percent. Lakes sites that were not assessed anc 
indicators for which no data was recorded are not included. Please refer to the Technical Appendix for further discussion. 


24 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 



































Chapter 3 


The Biological Condition of the Nation’s Lakes 


combines multiple characteristics to evaluate 
biological condition. In this instance, the two 
communities may be responding differently 
to the stresses impacting lakes or to different 
stresses. 

Stressors to Lake Biota 

In the aquatic environment, a stressor 
can be anything (chemical, biological or 
physical) that has the potential to impact its 
inhabitants by altering their surroundings 
outside their normal ecological range. There 
are many external occurrences that can alter 
a creature's ability to thrive, both natural and 
otherwise. Drought or rapid draw-down can 
be a stressor; contaminants (e.g., metals) 
can be a stressor; and human activity can 
be a stressor. An important dimension of the 
national lakes assessment is to evaluate key 
chemical and physical stressors of lake quality 
that, when altered, have the potential to 
impact lake biota. 

1. Chemical Stressors 

For the assessment, five of the eight 
chemical indicators of lake stress were 
evaluated. These are total phosphorus 
concentration, total nitrogen concentration, 
turbidity, acid neutralizing capacity (ANC), 
and dissolved oxygen concentration (DO). 

Phosphorus, Nitrogen, 
and Turbidity 

Phosphorus and nitrogen are critical 
nutrients required for all life. In appropriate 
quantities, these nutrients support the 
primary algal production necessary to support 
lake food webs. In many lakes, phosphorus 
is considered the "limiting nutrient," 
meaning that the available quantity of this 
nutrient controls the pace at which algae 
are produced in lakes. This also means that 
modest increases in available phosphorus can 
cause very rapid increases in algal growth. 


Some lakes are limited by nitrogen. In these 
lakes, modest increases in available nitrogen 
will yield the same effects. When excess 
nutrients from human activities enter lakes, 
cultural eutrophication is often the result. The 
culturally-accelerated eutrophication of lakes 
has a negative impact on everything from 
species diversity to lake aesthetics. 

Turbidity is a measure of light scattering, 
specifically, murkiness or lack of clarity. Lakes 
that are characterized by high concentrations 
of suspended soil particles and/or high 
levels of algal cells will have high measured 
turbidity. Turbidity in lakes is natural in 
some instances, resulting from natural soil 
deposition and resuspension within the lakes 
themselves. When human activities in lake 
watersheds and riparian zones increase soil 
erosion, increased turbidity often results 
in smothering of nearshore habitats by 
sediments and/or changing algae growth 
patterns. These changes affect biological and 
recreational conditions. 



Boat fully loaded for a day on an Oklahoma lake. 

Photo courtesy of Paul Koenig. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


25 














Chapter 3 


The Biological Condition of the Nation’s Lakes 


Findings for Nutrients 
and Turbidity 

Phosphorus, nitrogen, and turbidity are 
linked indicators that jointly influence both 
the clarity of water and the concentrations 
of algae in a lake. The levels of these 
three indicators vary regionally, as do the 
relationships between nutrients and turbidity, 
and between nutrients and algal growth. For 
phosphorus, nitrogen, and turbidity, lakes 
were assessed in relation to regionally- 
specific thresholds based on the distributions 
in a distinct set of reference lakes. 

Survey results show that slightly over half 
of the nation's lakes are in good condition 
with respect to phosphorus and nitrogen 
(Figure 7). Fifty-eight percent and 54% of 
lakes are not stressed for the two nutrients, 
respectively. For all lake classes there was 
no significant difference between phosphorus 


and nitrogen indicators. For both nutrients, 
there are no significant differences between 
natural lakes and man-made lakes. 

For turbidity, 78% of lakes are in good 
condition, 16% are in fair condition, and 6% 
are in poor condition. When comparing the 
natural lakes to the man-made lakes for this 
indicator, 75% of natural lakes are in good 
condition as compared to 81% of man-made 
lakes. 

Lake Acidification 

While not a widespread problem, lake 
acidification continues to be an important 
indicator of lake condition in a small number 
of areas around the country. Acid rain and 
acid mine drainage are major sources of 
acidifying compounds and can change the 
pH of lake water, impacting fish and other 
aquatic life. Acid neutralizing capacity 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 



25.8% 



120 . 


7% 



Total Nitrogen 




0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 

Percentage of Lakes 

l — ..I Good i i Fair i^SI Poor 


Figure 7. Phosphorus, nitrogen, and turbidity in three lake classes. 


26 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 







































Chapter 3 


The Biological Condition of the Nation’s Lakes 


ANC Assessment Thresholds 

Non-acidic 

>50 peq ANC 

Acidic-natural 

< 50 peq ANC 
and DOC < 5 
mg/L 

Anthropogenically 

acidified 

<0 peq ANC and 
DOC < 5 mg/L 


(ANC) serves as an indicator for sensitivity 
to changes in pH. The ANC of a lake is 
determined by the soil and underlying geology 
of the surrounding watershed. Lakes with 
high levels of dissolved bicarbonate ions (e.g., 
limestone watersheds) are able to neutralize 
acid depositions and buffer the effects of acid 
rain. Conversely, watersheds that are rich in 
granites and sandstones and contain fewer 
acid-neutralizing ions have low ANC and 
therefore a predisposition to acidification. 

Maintaining stable and sufficient ANC is 
important for fish and aquatic life because 
ANC protects or buffers against drastic 
pH changes in the waterbody. Most living 
organisms, especially aquatic life, function at 
the optimal pH range of 6.5 to 8.5. Sufficient 
ANC in surface waters will buffer acid rain 
and prevent pH levels from straying outside 
this range. In naturally acidic lakes, the ANC 
may be quite low, but the presence of natural 
organic compounds in the form of dissolved 
organic carbon, or DOC, can mitigate the 
effects of pH fluctuations. 

Findings for Lake Acidification 

Results from the NLA indicate that almost 
all, or 99%, of the nation's lakes can be 
classified as in good condition with respect 
to ANC (Figure 8). When looking at these 
results, however, it is also important to note 
that although the NLA indicates that lake 
acidification is not a widespread problem, 


acidification on a smaller scale, i.e., "hot 
spots/' do occur. While only a relatively small 
proportion of lakes may be impacted by 
acidification, the effects of acidification in the 
impacted lakes, and the contribution of acidity 
to other stressors, can be severe in specific 
geographic regions. 

Dissolved Oxygen 

Dissolved oxygen, or DO, is considered 
one of the more important measurements 
of water quality and is a direct indicator of a 
lake's ability to support aquatic life. Aquatic 
organisms have different DO requirements 
for optimal growth and reproduction. 
Decreases in DO can occur during winter or 
summer when the available dissolved oxygen 
is consumed by aquatic plants, animals, 
and bacteria during respiration. While each 
organism has its own DO tolerance range, 
generally levels below 3 mg/L are of concern. 
Conditions below 1 mg/L are referred to as 
hypoxic and are often devoid of life. 



(49,546) 


Natural 

(29,308) 


Acidification 


Number 
of Lakes 


Man-Made 

(20,238) 


1 1 


99 . 0 % 

49,036 

| 1 . 0 % 

510 

0 % 

0 

99 . 2 % 

29.073 

0 . 8 % 

235 

0 % 

0 

98 . 6 % 

19,963 

■|) 1 . 4 % 

275 

0 % 

0 


0 20 40 60 80 100 

Percentage of Lakes 

l l Non-Arid ir. I ) Acidic-Natural 

■I Acidic-Human Caused 


Figure 8. Acid neutralizing capacity for lakes of the U.S. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


27 























Chapter 3 


The Biological Condition of the Nation’s Lakes 


Findings for Dissolved Oxygen 

For the NLA, DO assessment thresholds 
were established as high (> 5 mg/L), 
moderate (>3 to <5), and low (<3 mg/L), 
and were based on measurements from 
the top two meters in the middle of the 
lake (Figure 9). Eighty-eight percent of the 
country's lakes display high levels of DO and 
are in good condition based on the surface 
waters sampled (Figure 9). Natural lakes 
perform slightly better than the nation as a 
whole with 94% in good condition. Man-made 
lakes results show 80% with high levels of 
DO. 


These findings indicate that, in general, 
low DO is not a chronic problem near the lake 
surface, which was not surprising given the 
sampling approach used in the survey. Future 
surveys may be able to more adequately 
address DO conditions in the bottom waters 
of lakes where low DO conditions are more 
likely to occur first. 

2. Physical Stressors 

The condition of lakeshore habitats (Figure 
10) provides important information relevant 
to lake biological health. For the NLA, physical 
habitat condition was assessed based on 
observations for four indicators: 1) lakeshore 
habitat, 2) shallow water habitat, 3) physical 
habitat complexity (an index of habitat 
condition at the land-water interface), and 
4) human disturbance (extent and intensity 
of human activity). In assessing the physical 
habitat complexity indicator, NLA analysts 
looked at not only the total amount of cover 
present but also the diverse types of cover 
and the complex nature of potential ecological 
niches. For each lake habitat indicator, values 
were compared to the distribution of the 
indicator value in the reference sites. 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 


Number 



0 20 40 60 80 100 


Percentage of Lakes 


High (> 5 mgl/l) i i Moderate (> 3 - 5 mg/L) 

Low (<= 3 mg/L) I I No Data 


Figure 9. Dissolved oxygen for lakes of the U.S. 


Lakeshore Habitat 

The lakeshore habitat indicator examines 
the amount and type of shoreline vegetation. 
It is based on observations of three layers 
of coverage (understory grasses and forbs, 
mid-story non-woody and woody shrubs, and 
overstory trees). In general, lakeshores are 
in better condition when shoreline vegetation 
cover is high in all three layers. It is important 
to note, however, that not all three layers 
naturally occur in all areas of the country. For 
example, in the Northern Plains areas, there 
is typically no natural overstory tree cover. 
Similarly, in some areas of the intermountain 
west, steep rocky shores are the norm for 
high-mountain and/or canyon lakes. These 
natural features have been factored into the 
calculation of the lakeshore habitat indicator. 


28 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 















Chapter 3 


The Biological Condition of the Nation’s Lakes 



euphotic zone 


Figure 10. Schematic of a lakeshore. 


Shallow water habitat 

The shallow water habitat indicator 
examines the quality of the shallow edge of 
the lake by utilizing data on the presence 
of living and non-living features such as 
overhanging vegetation, aquatic plants 
(macrophytes), large woody snags, brush, 
boulders, and rock ledges. Lakes with greater 
and more varied shallow water habitat are 
typically able to more effectively support 
aquatic life because they have more, and 
more complex, ecological niches. Like the 
lakeshore habitat indicator, the shallow water 
indicator is related to conditions in reference 
lakes and is modified regionally to account for 
differing expectations of natural condition. 


Physical habitat complexity 

The third indicator, physical habitat 
complexity, combines data on from the 
lakeshore and shallow water interface. This 
indicator estimates the amount and variety 
of all cover types at the water's edge. Like 
the other indicators, this index is related 
to conditions in reference lakes and is 
modified regionally to account for differing 
expectations of natural condition. 


National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 


29 



















Chapter 3 


The Biological Condition of the Nation’s Lakes 



Lakeshore Habitat of Lakes 


National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 



5 . 5 % 

22,546 


8,832 

% 

17,807 

50 . 4 % 

14,775 


4,843 

6 

9,547 

4 % 

7,771 


3,989 

oo 

nO 

0 s 

8,260 


“1 -r- 

0 20 40 60 80 100 

Percentage of Lakes 

I n Good I I Fair Fffin Poor 

Figure 11. Lakeshore habitat for lakes of the U.S. as percent 
of lakes in three condition classes. 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 


Shallow Water Habita 



mmmm 




■ 


20 . 0 % 

24 . 5 % 


58 . 7 % 


61 . 6 % 


I 54 . 6 % 


Number 
of Lakes 


29,905 

10,133 

9,980 

18,051 

6,086 

5,025 

11,044 

4,047 

4,954 


0 20 40 60 80 100 

Percentage of Lakes 

i i Good i i Fair Poor 


Figure 12. Shallow water habitat for lakes of the U.S. as 
percent of lakes in three condition classes. 


Findings for Habitat Integrity 

The findings for the three habitat stressor 
indicators are depicted in Figures 11, 12 
and 13. Nationally, 46% of lakes exhibit 
good lakeshore habitat condition, while 
18% of lakes are in fair condition and 36% 
are in poor condition. With respect to the 
shallow water areas of lakes, 59% of lakes 
exhibit good habitat condition, while 21% of 
lakes are in fair condition, and 20% are in 
the most disturbed, or poor condition. For 
physical habitat complexity of the land/water 
interface, 47% of lakes are in good condition, 
20% of lakes are in fair condition, and 32% 
are in poor condition. For all three habitat 
indicators, more natural lakes support healthy 
combined habitat condition than man-made 
lakes. 


Lakeshore Human Disturbance 

In the above discussion of the lakeshore 
environment, the condition of lakes was 
described in terms of habitat integrity in both 
the lakeshore and shallow water areas of the 
lake. The fourth indicator of physical habitat 
is lakeshore human disturbance and reflects 
direct human alteration of the lakeshore itself. 
These disturbances can range from minor 
changes (such as the removal of trees to 
develop a picnic area) to major alterations 
(such as the construction of a large lakeshore 
residential complex complete with concrete 
retaining walls and artificial beaches). The 
effects of lakeshore development on the 
quality of lakes include excess sedimentation, 
loss of native plant growth, alteration of 
native plant communities, loss of habitat 
structure, and modifications to substrate 
types. These impacts, in turn, can negatively 
affect fish, wildlife, and other aquatic 
communities. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 






















































Chapter 3 


The Biological Condition of the Nation’s Lakes 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 


Physical Habitat 
Complexity 



Number 
of Lakes 


46.8% 


52.3% 


28.5% 


1 

_ 


<38.8% 


22 . 2 % 



37.9% 


23,181 

9,956 

16,033 

15,327 

5,468 

8,366 

7,854 

4,488 

7,667 


0 20 40 60 80 100 

Percentage of Lakes 

[ I Good i i Fair i » Poor 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 


Lakeshore Disturbance of Lakes 




I-1 56.9% 



17,259 

23,600 

8 364 

13,586 

12,091 

3,490 

3,673 

11,509 

4,874 


20 40 60 80 100 

Percentage of Lakes 

Z3 Good I I Fair ■■§ Poor 


Figure 13. Physical habitat complexity for the lakes of the 
U.S. as percent of lakes in three condition classes. 


Figure 14. Lakeshore disturbance for lakes of the U.S. as 
percent of lakes in three conditions classes. 


Findings for Lakeshore Disturbance 

Across the lower 48 states, 35% of lakes 
exhibit good conditions representative of 
relatively low human disturbance levels, while 
48% of lakes exhibit moderate disturbance, 
and 17% exhibit poor, or highly disturbed 
conditions (Figure 14). In contrast to the 
other three habitat indicators, the percentage 
of natural lakes that have minimal lakeshore 
disturbance is substantially higher than that 
of man-made lakes. Forty-six percent of 
natural lakes are in good condition compared 
to 18% of man-made lakes. These findings 
also show that there are twice as many man¬ 
made lakes with high lakeshore disturbance 
(poor condition) as natural lakes. 


Ranking of Stressors 

An important key function of the national 
assessments is to provide a perspective on 
key stressors impacting biological condition in 
lakes and rank them in terms of the benefits 
expected to be derived from reducing or 
eliminating these stresses. For the NLA, 
analysts used three approaches to rank 
stressors. The first looks at how extensive or 
widespread any particular stressor is, e.g., 
how many lakes have excess phosphorus 
concentrations. The second examines the 
severity of the impact from an individual 
stressor when it is present, e.g., how 
severe is the biological impact when excess 
phosphorus levels occur. Ranking ultimately 
requires taking both of these perspectives 
into consideration. The third approach is 
attributable risk, which is a value derived 
by combining the first two risk values into a 
single number for ranking across lakes. 


National Lakes Assessment A Collaborative Survey of the Nation's Lakes 


31 













































Chapter 3 


The Biological Condition of the Nation’s Lakes 


Throughout this section, the stressors 
are assessed and reported independently 
and as such do not sum to 100%. Most lakes 
are likely to experience multiple stressors 
simultaneously which can result in cumulative 
effects rather than those elicited by a single 
stressor. 


a small area (/.e., hot spots) or that occur 
over a wide area but are spread out have a 
low relative extent. It is important for water 
resource managers to take into account the 
extent of the stressor when setting priority 
actions at the national, regional, and state 
scale. 


Relative Extent 

Relative extent is a way of evaluating 
how widespread and common a particular 
stressor is among lakes. A stressor with a 
high relative extent indicates a significant 
concern. Conversely, stressors that occur over 


Nationally, the most widespread stressors 
measured as part of the NLA are those that 
affect the shoreline and shallow water areas, 
which in turn can affect biological condition. 
Results from the NLA show that the most 
widespread of these is the alteration of 
lakeshore habitat. 


Lakeshore Habitat 
Physical Habitat Complexity 
Shallow Water Habitat 
National Total Nitrogen 


(49,546) 


Total Phosphorus 
Lakeshore Disturbance 
Turbidity 


Dissolved Oxygen 


Lakeshore Habitat 
Physical Habitat Complexity 
Shallow Water Habitat 
Total Nitrogen 

Total Phosphorus 
Lakeshore Disturbance 
T urbidity 
Dissolved Oxygen 


Natural 

(29,308) 


Lakeshore Habitat 


Physical Habitat Complexity 

Man-Made Shallow Water Habitat 


(20,238) 


Total Nitrogen 
Total Phosphorus 
Lakeshore Disturbance 
T urbidity 
Dissolved Oxygen 


Relative Extent JS 



I 40.8% 
O -1 37.9% 



17,807 

16,033 

9,980 

9,467 

9,006 

8,364 

3,100 

632 


9,547 

8,366 

5,025 

5,690 

4,955 

3,490 

1,148 

153 


8,260 

7,667 

4,954 

3,777 

4,051 

4,874 

1,952 

480 


0 20 40 60 80 100 

Percentage of Lakes Rated 
Poor for Each Stressor 


Relative Risk to 
Biological Condition 



Attributable Risk 


42.5% 



147.1% 


141.9% 


29.3% 



0 


2 4 6 8 0 20 40 60 80 100 

Relative Risk Percentage of Lakes 


Figure 15. Relative extent of poor stressors conditions. Relative risks of impact to plankton O/E and Attributable risk (combining Relative 
extent and Relative risk). 


32 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 

































































































Chapter 3 


The Biological Condition of the Nation’s Lakes 


Thirty-six percent of lakes nationally 
have poor lakeshore habitat (Figure 15, left 
graph). The second most prevalent stressor 
is physical habitat complexity, which is poor 
in 32% of lakes nationally. Total nitrogen 
and total phosphorus ranked fourth and fifth, 
respectively, in terms of how widespread 
excess levels are across the country. 

The ranking of these stressors according 
to extent is similar across natural and 
man-made lakes with most stressors being 
more widespread in man-made lakes (e.g., 
lakeshores with poor habitats occurring at 
41% of man-made lakes compared with 33% 
of natural lakes). 

Relative Risk 

The evaluation of relative risk is a way 
to examine the severity of the impact of 
a stressor when it occurs. Relative risk is 
used frequently in the human health field. 

For example, a person who smokes is 10- 
20 times more likely to get and die of lung 
cancer 4 . Similarly, one can examine the 
likelihood of having poor biological conditions 
when phosphorus concentrations are high 
compared with the likelihood of poor biological 
conditions when phosphorus concentrations 
are low. When these two likelihoods are 
quantified, their ratio is called the relative 
risk. For the NLA, only the relative risk of 
stressor to poor conditions is presented. 

Results of the relative risk analyses are 
presented in the middle graph of Figure 15. 
The highest relative risk nationally was found 
for lakeshore habitat disturbance with a 
relative risk just over 3. This means that lakes 
with poor surrounding vegetation are about 3 
times more likely to also have poor biological 
conditions, as defined for this assessment. 

The remaining stressors, with the exception of 



Survey crew member records shoreline habitat data. 

Photo courtesy of Texas Commission of Environmental Quality. 


dissolved oxygen and lakeshore disturbance, 
have relative risks near 2 (/.e., twice as 
likely to have poor biological conditions). The 
relative risks for stressors in natural lakes 
appear consistently greater than the relative 
risk values for man-made lakes. 

Attributable Risk 

As mentioned, attributable risk is 
derived by combining the relative extent 
and the relative risk into a single number 
for the purposes of ranking. Conceptually, 
attributable risk provides an estimate of 
the proportion of poor biological conditions 
that could be reduced if poor conditions of a 
particular stressor were eliminated. This risk 
value represents the magnitude or importance 
of a potential stressor and one that can be 
ranked and prioritized for policy makers and 
managers. 

Estimates for attributable risk based on 
the planktonic O/E indicator of biological 
condition are presented in right graph of 
Figure 15. Lakeshore habitat alteration has 
the highest attributable risk for plankton taxa 
loss while other stressors (with the exception 
of lakeshore disturbance, turbidity and 


4 Centers for Disease Control, http://www.cdc.aov/cancer/lunq/risk factors.htm 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


33 









Chapter 3 


The Biological Condition of the Nation’s Lakes 


dissolved oxygen) have similar attributable 
risk values. Thus one might expect that 
to improve lake condition to the greatest 
extent, lakeshore vegetative habitat would 
have to be increased to the point that it is 
no longer a stressor. Natural lakes show a 
slightly different pattern in attributable risk 
with lakeshore habitat being a high priority 
followed closely by total nitrogen, total 
phosphorus and physical habitat complexity. 
For man-made lakes, three of the four habitat 
indicators rank the highest in attributable risk. 


Human shoreline disturbance is an important stressor in lakes. 

Photo courtesy of Great Lakes Environmental Center. 



Lakeshore Alteration Stress 

By Kellie Merrell, VT Department of Conservation 

Transformation of lakeshores from natural forested and wetland cover to lawns and sandy beaches, 
accompanied by residential homes development (and redevelopment) is a stressor to many lakes. In a survey 
of 345 lakes in the Northeast during the early 1990s, the U.S. Environmental Protection Agency and U.S. 

Fish and Wildlife Service determined that stress from shoreline alteration was a more widespread problem 
than eutrophication and acidification. In recent years, many state agencies have documented the effects of 
shoreline development on nearshore and shallow water habitat quality with notable results. 

As lakeshores are converted from forests to lawns, lakes are impacted by impervious surfaces, enhanced 
runoff, less shading, and in most cases, more abundant aquatic plant growth in shallow areas. Shallow water 
habitat is further simplified by the direct removal of woody structure, and interruption in the resupply of this 
critical habitat component. The Wisconsin Department of Natural Resources has estimated that unbuffered 
developed sites contribute five times more runoff, seven times more phosphorus and 18 times more sediment 
to a lake than the naturally forested sites. 

This alteration of the nearshore and shallow water habitat affects a variety of both terrestrial and aquatic 
wildlife and has been described in the literature. Green frog, dragonfly, and damselfly populations decline. 

The nesting success and diversity of fish species also declines, with sensitive native species being replaced 
by more tolerant species. Turtles lose basking sites and corridors to inland nest sites. Bird composition shifts 
from insect-eating to seed-eating species. Even white-tailed deer are affected, with reduction in winter browse 
along shorelines reducing winter carrying capacity. The removal of conifers along shores also reduces shoreline 
mink activity. Ultimately, the cumulative effects of lakeshore development have negative implications for many 
species of fish and wildlife. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 










CHAPTER 4 


SUITABILITY FOR RECREATION 



IN THIS CHAPTER 

► Algal Toxins 

► Contaminants in Fish Tissue 

► Pathogen Indicators 









Chapter 4 


Suitability for Recreation 



Chapter 4 

Suitability for Recreation 

Another perspective on lake condition 
views the quality of a lake in terms of its 
suitability or safety for recreational use. Lakes 
are used for a wide variety of recreational 
opportunities that include swimming, 
waterskiing, windsurfing, fishing, boating, 
and many other activities. However, a number 
of microbial organisms, algal toxins, and 
other contaminants present in lakes can 
make people sick. NLA analysts assessed 
three indicators with respect to recreational 
condition: 1) microcystin - a type of algal 
toxin, 2) cyanobacteria - a type of algae 
that often produces algal toxins, and 3) 
chlorophyll-a — a measure of all algae 
present. Results from a companion study of 
contaminants in fish tissue are also discussed. 
Samples were also collected for pathogens 
and sediment mercury; however, results 
for these two indicators are unavailable 
as of publication of this report and will be 
presented in supplemental reports available 
on http://www.eDa.Qov/lakessurvev/ . 


Algal Toxins 

One group of phytoplankton, 
cyanobacteria (also called blue-green 
algae) are a natural part of all freshwater 
ecosystems. Eutrophication in lakes often 
results in conditions that favor their growth 
and cyanobacterial blooms frequently occur. 
Cyanobacterial blooms can be unsightly, often 
floating in a layer of decaying, odiferous, 
gelatinous scum. Many types of cyanobacteria 
have the potential to produce cyanotoxins, 
and several different cyanotoxins may be 
produced simultaneously. In assessing the risk 
of exposure to algal toxins for recreational 
safety, it is important to remember that algal 
density, i.e., chlorophyll-a concentrations 
and cyanobacteria cell counts, serve as 
proxies for the actual presence of algal 
toxins. This is because not all phytoplankton 
are cyanobacteria and not all cyanobacteria 
produce cyanotoxins. 

Although there are relatively few 
documented cases of severe human health 
effects, exposure to cyanobacteria or their 
toxins may produce allergic reactions such 


36 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 






































Chapter 4 


Suitability for Recreation 


as skin rashes, eye irritations, respiratory 
symptoms, and in some cases gastroenteritis, 
liver and kidney failure, or death. The most 
likely exposure route for humans is through 
accidental ingestion or inhalation during 
recreational activities, though cyanotoxins 
are also cause for concern in drinking water. 
Cyanotoxins can also kill livestock and 
pets that drink affected water. While many 
varieties of cyanotoxin exist, microcystin, 
produced by Microcystis taxa, is currently 
believed to be the most common in lakes. 
Microcystin is a potent liver toxin, a known 
tumor promoter, and a possible human 
carcinogen. 

Because of the potential for human 
illness, several states have issued guidelines 
for recreational use advisories associated with 
the presence of microcystin or associated 
indicators. These guidelines vary and rely on 
visual observations of algal scums, measured 
chlorophyll-a concentrations, cyanobacteria 


Table 1. World Health Organization thresholds of risk associated with potential 
exposure to cyanotoxins. 


Indicator 

(units) 

Low Risk 

of Exposure 

Moderate 

Risk 

of Exposure 

High Risk 
of Exposure 

Chlorophyll-a 

(M9/L) 

<10 

10 - <50 

>50 

Cyanobacteria 
cell counts (#/L) 

< 20,000 

20,000 - 
<100,000 

> 100,000 

Microcystin 

(pg/L) 

<10 

10 - <20 

>20 


cell counts, and/or direct measurements of 
microcystin. While EPA does not presently 
have water quality criteria for microcystin, 
cyanotoxin, or any other algal toxins, the 
World Health Organization (WHO) has 
established recreational exposure guidelines 
for chlorophyll-a, cyanobacterial cell counts, 
and microcystin (Table 1). 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 


Chlorophyll a 



67.3°/< 


h 

H 21 

• 

0.6% 


45.8% 



Cyanobacteria 



Microcystin Risk 



-1 0.7% 


0 . 2 % 



-11.3% 


0.3% 


0 % 

0 % 



-i-1-r 


0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 

Percentage of Lakes 

Low Risk I I Moderate Risk High Risk 


Figure 16. Percent of lakes, using three algal toxin indicators. In the first two graphs the percentage numbers indicate the risk or exposure to 
algal toxins associated with the presence of chlorophyll-a and cyanobacteria, not the risk of exposure to cholorphyll-a and cyanobacteria per 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 
















































Chapter 4 


Suitability for Recreation 


These thresholds, along with the presence 
or absence of microcystin, were used to 
assess the condition of lakes of the nation 
with respect to this indicator suite. A lake 
that is in good condition exhibits a low risk of 
potential exposure. Conversely, a lake in poor 
condition has a high exposure potential. 

Using the WHO thresholds, the level 
of risk associated with the exposure to 
algal toxins varied by indicator (Figure 16). 
Using the cyanobacteria cell count as the 
indicator, 27% of lakes nationwide pose a 
high or moderate risk for potential exposure 
to algal toxins. There was no significant 
difference in the proportion of natural and 
man-made lakes with high or moderate 
exposure risks for cyanobacteria. Based on 
chlorophyll-a concentration, 41% of lakes 
pose a high or moderate exposure potential to 
algal toxins. 

It is important to note, however, that 
while the risk of exposure is extremely low, 
microcystin was present in 30% of lakes 
nationally (Figure 17). This could potentially 
have wide ranging impacts on human 
health and the swimmability of many lakes. 
When interpreting the data of this first 
ever national-scale study of microcystin in 
lakes, it is necessary to consider how the 
sampling was conducted. During the 2007 
survey, microcystin samples were collected 
at mid-lake, in open water. However, large 
windblown accumulations of cyanobacteria 
often occur at nearshore areas in lakes and 
it is the concentrations along the lake's 
edge that are of most concern to municipal 
health officials. Some studies indicate that 
cell counts and cyanotoxin concentrations 
are greater in nearshore scums than in open 
water areas. However, concentrations large 
enough to cause human health concerns may 
still occur in open waters (with or without 
surface accumulations or scums). Sampling 
at mid-lake provides a conservative estimate 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 


Microcystin 

Number 

Presence of Lakes 



30 . 1 % 



30 . 6 % 



29 . 5 % 


-i-1-1-r 


14,929 


8,955 


5,975 


0 20 40 60 80 100 

Percentage of Lakes 

Figure 17. Occurrence of microcystin in lakes. 


and because of this, the NLA results may 
underestimate certain types of recreational 
exposure when accumulations or scums are 
present. 

Another important point to consider 
when looking at the data is whether the 
single sample of microcystin truly represents 
what is in the lake. Chlorophyll-a levels, 
cyanobacteria densities, and cyanotoxin 
concentrations may change quite rapidly, 
depending on bloom intensity and weather 
conditions. The concentrations of microcystin 
measured on one particular day may over 
or underestimate season-wide central 
tendencies. The NLA is not intended to assess 
the specific condition of any given lake, but 
rather provide information on the general 
conditions across the population of lakes. 
Finally, it is currently unknown how well 
microcystin occurrence correlates with the 
occurrence of other classes of cyanotoxins 


38 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 

















Chapter 4 


Suitability for Recreation 


that were not measured, or how human 
health risks might be altered because of toxin 
mixtures. While the survey results are a good 
start in our understanding, much more is to 
be learned about algal toxins in lakes. 

Contaminants in Lake Fish Tissue 

Fish acquire contaminants and 
concentrate them in their tissues by uptake 
from water (bioconcentration) and through 
ingestion (bioaccumulation). Fish can often 
bioaccumulate chemicals at levels of more 
than a million times the concentration 
detected in the water column. 

In a study conducted by the Office of 
Water's Office of Science and Technology, EPA 
surveyed contaminants in lake fish tissue. The 
National Study of Chemical Residues in Lake 
Fish Tissue characterized contaminant levels 
in fillet tissue for predators and in whole 
bodies for bottom-dwelling fish species. The 
study targeted pollutants that were classified 
as persistent, bioaccumulative, and toxic 
(PBT) chemicals, including mercury, arsenic, 
PCBs, dioxins and furans, DDT, and chlordane. 
This survey provided data to develop national 
estimates for 268 PBT chemicals in fish 
tissue from lakes and reservoirs in the 48 
continental states (excluding the Great Lakes 
and the Great Salt Lake). 

The study focused on fish species that 
are commonly consumed in the study area, 
have a wide geographic distribution, and 
potentially accumulate high concentrations of 
PBT chemicals. Fish samples were collected 
over a 4-year period (2000-2003) from 500 
randomly selected lakes and reservoirs, which 
ranged in size from 2.5 acres (1 hectare) to 
900,000 (365,000 hectares), were at least 3 
feet (1 meter) deep, and had permanent fish 
populations. 


The data show that mercury, PCBs, 
dioxins and furans, and DDT are widely 
distributed in lakes and reservoirs across the 
country. Mercury and PCBs were detected 
in all fish samples (Figure 18). Dioxins and 
furans were detected in 81% of the predator 
samples and 99% of the bottom-dwelling fish 
samples. DDT was detected in 78% of the 
predator samples and 98% of the bottom¬ 
dwelling samples. Cumulative frequency 
distribution plots showed that established 
human consumption limits were exceeded 
in 49% of the sampled lakes for mercury, 
in 17% of the lakes for total PCBs, and in 
8% of the lakes for dioxins and furans. In 
contrast, 43 targeted chemicals were not 
detected in any sample. Full results from this 
study can be found at http://www.epa.aov/ 
waterscience/fishstudv. 


Mercury 


PCBs 


0 20 40 60 80 100 

Percentage of Lakes 

For Mercury: For PCBs: 

| < 300 ppb J < 12 ppb 

| > 300 ppb | > 12 ppb 

Figure 18. Percentage predator fish with mercury and PCB levels 
above (red) and below (green) EPA recommended limits. 


Contaminants in Predator Fish 



National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 


39 




















Chapter 4 


Suitability for Recreation 


Pathogen Indicators 

Enterococci are believed to provide a 
better indication of the presence of pathogens 
than more traditional indicators for fecal 
coliform. Enterococci are bacteria that live 
in the intestinal tracts of warm-blooded 
creatures, including humans. 

They are most frequently found in soil, 
vegetation, and surface water because of 
contamination by animal excrement. Most 
species of enterococci are not considered 
harmful to humans. However, the presence 
of enterococci in the environment indicates 
the possibility that other disease-causing 
agents also carried by fecal material may be 
present. Epidemiological studies of marine 
and freshwater beaches have established 
a relationship between the density of 
enterococci in the water and the occurrence 
of gastroenteritis in swimmers. 

For the NLA, enterococci were measured 
using a method to assess ambient 
concentrations. This Quantitative Polymerase 
Chain Reaction (qPCR) method quantifies 
DNA that is specific to enterococci. Published 
epidemiological studies report a clear 
relationship between levels of qPCR-measured 
enterococci and sickness. EPA research is still 
underway to develop health-based thresholds 
for interpreting qPCR results. 


Analyzing phytoplankton samples. 

Photo courtesy of EcoAnalysts. 




40 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 









HIGHLIGHT 


Atmospheric Contaminants: 
Mercury and Acid Rain 


Neil C. Kamman 

Vermont Department of Environmental Conservation 


Of the many stressors that affect lakes, atmospheric contaminants are perhaps the most difficult to 
address. This is because sources of atmospheric contaminants are often hundreds or even thousands 
of miles from the lakes into which the contaminants are ultimately deposited. The intertwined issues of 
freshwater acidification and mercury contamination are not new. The popular press began reporting on 
acid rain in the 1970s. It took another 10-15 years for the press to also focus on mercury. Today, many 
people are aware of both issues, yet often do not fully comprehend nor appreciate the degree to which the 
two are linked. In the case of both these pollutants, the cycle is initiated by emissions into the air. 

Mercury is a naturally occurring metal that is found in the environment in many forms, all of which 
are toxic to aquatic life in varying degrees. The release of mercury to the environment is enhanced by 
human activities such as the combustion of fossil fuels, such as coal and petroleum. In the U.S. the largest 
sources of mercury are coal-fired generation or utility boilers, followed by waste incinerators. Mercury is 
present in many household items, notably thermostats and fluorescent lamps, and is released when these 
items end up in landfills or incineration facilities. Depending on its chemical form, air-borne mercury may 
remain in the atmosphere for a period of minutes (as reactive gaseous mercury), days (as particulate 
mercury), or weeks or years (as gaseous elemental mercury). 

Methylmercury, one of the most toxic forms of mercury, can be prevalent in fish and has documented 
adverse health effects on humans. The U.S. Centers for Disease Control and Prevention estimates that 
up to 6% of women of childbearing age have blood mercury levels in excess of established safety levels. 
Fish and fish-eating wildlife such as the common loon and American bald eagle are also at risk from 
mercury toxicity. While the mercury cycle in lakes is quite complex, there are five basic stages: emission, 
deposition, methylation*, bioaccumulation, and finally sequestration to lake sediments. 

Lake acidification is most commonly caused by acidic deposition (rain, snow and dust). The acidic 
deposition pathway begins with the release into the air of acid-forming chemicals, most notoriously sulfur 
dioxide and nitrogen oxides, and ends when sulfuric and nitric acids are deposited to the landscape. Sulfur 
dioxide, like mercury, results largely from the burning of fossil fuels. Some forms of coal are very rich in 
sulfur, and poorly controlled facilities released massive quantities, particularly during the period 1960- 
1992. Both sulfur dioxide and nitrogen oxides are common components of vehicular emissions. Once 
emitted, these two compounds undergo complex atmospheric transformations, resulting in rain and snow 
that contain dilute concentrations of nitric and sulfuric acids. Thankfully, the Clean Air Act Amendments of 
1990 have resulted in profound reductions in acid-forming precursors. In very sensitive regions, however, 
lakes remain at risk for acidification even with reduced levels of acid rain. 

In one sense, the process of lake acidification is not as complex as that of mercury accumulation in 
that there is neither methylation nor bioaccumulation of the acids. Yet acidification has more pernicious 
effects that can exacerbate mercury problems. Acidification of watersheds renders the watersheds more 
efficient at creating and transporting methylmercury to lakes, along with other soil-bound toxic metals 
such as aluminium. Moreover, acidification of the lakes themselves renders the bioaccumulation of 
methylmercury more efficient. Therefore, acidic lakes: 1) receive more mercury from their watershed, 2) 
have more of the mercury in the toxic methylated form, and 3) have more efficient bioaccumulation of the 
methylmercury. 

The natural and biologically-mediated process by which mercury is transformed into toxic organic methylmercury. 





National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 









Studies throughout the United States, Canada, Russia, and Scandinavia all show a very strong 
connection between lake acidification and mercury bioaccumulation. Researchers have documented the 
occurrence of mercury hotspots in various parts of the U.S. and attribute these to one of three basic 
causes — proximity to poorly-controlled emissions sources, water level management in reservoirs, or acid 
sensitive landscapes. In regions of North America where lake acidification is in fact already improving, 
minor reductions in mercury in fish and fish-eating wildlife can be anticipated. Much more consequential 
reductions in environmental mercury contamination are expected as EPA and states strive to control 
mercury emissions from coal-fired utilities and other sources. 



Mercury Bioaccumulation in Lakes 




Mercury enters a lake by: 

*• Direct deposition 
■- Flow through wetlands 

Subsurface flow through soils 
— Runoff through streams 


L* / ' * I IT, J ' 

m f 2> • »,.v , 

' t’ 






IOCS 


Methyl Mercury 
Increases up the 
Food Chain 


% Methyl 50 % 
mercury 


Methyl mercury Water Phytoplankton Zooplankton Plant-eating fish 

btoaccumulation 

1 


Fish-eatng fish 


Loom 


million x 


10 million x 


Graphical depiction of methylmercury bioaccumulation in lake biota. This figure is reproduced from the Hubbard 
Brook Research Foundation’s ScienceLinks publication Mercury Matters: Linking Mercury Science with Public 
Policy in the Northeastern United States. Used with permission. 












42 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 
















































CHAPTER 5 


TROPHIC STATE OF LAKES 







Photo courtesy of USEPA Region 10 


IN THIS CHAPTER 


► Findings for Trophic State 






Chapter 5 


Trophic State of Lakes 



Photo courtesy of Great Lakes Environmental Center 


Chapter 5 

Trophic State of Lakes 

The third approach to assessing the 
condition of lakes is to look at lakes with 
respect to their primary production. Trophic 
state depicts biological productivity in lakes. 
Lakes with high nutrient levels, high plant 
production rates, and an abundance of plant 
life are termed eutrophic, whereas lakes 
that have low concentrations of nutrients, 
low rates of productivity and generally low 
biomass are termed oligotrophic. Lakes that 
fall in between are mesotrophic, and those 
on the extreme ends of the scale are termed 
hypereutrophic or ultra-oligotrophic. Lakes 
exist across all trophic categories; however 
hypereutrophic lakes are usually the result 
of excessive human activity and can be an 
indicator of stress conditions. 

There is no ideal trophic state for lakes 
as a whole since lakes naturally fall in 
all of these categories. Additionally, the 
determination of "ideal" trophic state depends 
on how the lake is used or managed. For 


example, an oligotrophic lake is a better 
source of drinking water than a eutrophic lake 
because the water is easier or less expensive 
to treat. Swimmers and recreational users 
also prefer oligotrophic lakes because of their 
clarity and aesthetic quality. Eutrophic lakes 
can be biologically diverse with abundant fish, 
plants, and wildlife. For anglers, increased 
concentrations of nutrients, algae, or aquatic 
plant life generally result in higher fish 
production. 

Eutrophication is a slow, natural part 
of lake aging, but today human influences 
are significantly increasing the amount of 
nutrients entering lakes. Human activities 
such as poorly managed agriculture or 
suburbanization of lakeshores can result 
in excessive nutrient concentrations 
reaching lakes. This can lead to accelerated 
eutrophication and related undesirable effects 
including nuisance algae, excessive plant 
growth, murky water, odor, and fish kills. 


44 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 























Chapter 5 


Trophic State of Lakes 


Findings for Trophic State 

For the NLA, the trophic state is 
characterized using nationally-consistent 
chlorophyll-a concentrations (Figure 19). 
Based on these thresholds, 13% of lakes 
are oligotrophic, 37% are mesotrophic, 30% 
are eutrophic, and 20% are hypereutrophic. 
The results also show that natural lakes tend 
towards mesotrophic conditions and man¬ 
made lakes towards eutrophic conditions. 

Many states and lake associations classify 
their lakes by trophic state using a variety 
of thresholds for nutrients (phosphorus 
or nitrogen), Secchi disk transparency, 
or chlorophyll-a, depending on the data 
available. For this assessment, NLA analysts, 
in consultation with a number of state and 
local lake experts, decided to base trophic 
state on chlorophyll-a concentrations. The 
group considered this indicator the most 
relevant and straightforward estimate of 
trophic state because it is based on direct 
measurements of live organisms, yet 
acknowledges that other indicators also could 
be used. Table 2 illustrates the percentages 
that would fall into the different trophic 
categories if different indicators were used. 
Total nitrogen and total phosphorus, (which 
ranked fourth and fifth in terms of how 
widespread excess levels are across the 
country) together or individually are primary 
drivers of eutrophication. 



National 

(49,546) 


Natural 

(29,308) 


Man-Made 

(20,238) 



Percentage of Lakes 


Oligotrophic (<= 2 ug/L) 
Mesotrophic (>2-7 ug/L) 
Eutrophic (>7 to 30 mg/L) 
Hypereutrophic (> 30 ug/L) 


Figure 19. Trophic state of lakes in the lower continental U.S. 


Table 2. Percent of U.S. lakes (natural and man-made) by trophic state, based on four alternative trophic state indicators. 


Indicator 

Oligotrophic 

Mesotrophic 

Eutrophic 

Hypereutrophic 

Chlorophyll-a 

12.8 

36.6 

30.1 

20 

Secchi 

transparency 

10.5 

22.5 

39.8 

18.4 

Total Nitrogen 

22.1 

37.5 

22.0 

18.4 

Total Phosphorus 

25.0 

28.8 

24.7 

21.4 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


45 
































































HIGHLIGHT 



Volunteer Power: 

Monitoring Lakes with Volunteers 


Hundreds of organizations monitor lakes in the U.S. using 
trained volunteers. Some volunteer groups are run by state 
environmental agencies. Others are managed by local residential 
lake associations determined to protect the quality of their 
local lake, pond or reservoir. Universities, often as part of U.S. 

Department of Agriculture Cooperative Extension, manage a 
number of statewide lake volunteer monitoring programs. In some 
states, trained volunteers are the leading source of consistent, 
long-term lake data. Volunteer-collected lake data are widely used 
in state water quality assessment reports, identification of impaired 
waters, local decision making, and scientific study. 

One national program designed to promote the use of 
volunteers in lake monitoring is the Secchi Dip-In fhttp://dipin. 
kent.edu/index.htnrU . Run by limnologist Dr. Robert Carlson of Kent 
State University since 1994, the Dip-In encourages individuals 
who are members of a volunteer monitoring program to measure 
lake transparency on or around the 4th of July and report their 
results on a national website. These values are used to assess 
the transparency of volunteer-monitored waters in the U.S. and 
Canada. One goal of the Dip-In is to increase the number and 
interest of volunteers in environmental monitoring and to provide 
national level recognition of the work that they perform. 

Volunteer Monitoring and the National Lakes Assessment 

The relationship between lake volunteer monitoring and the National Lakes Assessment (NLA) is in 
its earliest stages. However, volunteers did participate in a few states where links between volunteer 
programs and state monitoring staff were strong. The Vermont Department of Environmental Conservation 
(DEC) conducted its own statistically valid assessment of 50 lakes including NLA-selected lakes, about half 
of which are also routinely sampled by volunteers in the DEC-managed Vermont Lay Monitoring Program. 
Volunteers were informed ahead of time when NLA sampling crews were going to arrive, and in some 
cases were able to provide boats for the crews as well as welcome local advice regarding lake navigation 
and access. In Rhode Island, some volunteers conducted side-by-side sampling with the NLA crews for 
later analysis and comparison using Rhode Island Watershed Watch methods. Volunteers observed the 
sampling, assisted crews with equipment, provided firsthand knowledge of local lakes, and contacted 
news media to provide publicity. In Michigan, at two lakes also monitored by Michigan's Cooperative Lake 
Monitoring Program, volunteers sampled side-by-side with Michigan Department of Environmental Quality 
staff and NLA survey crews. Local newspaper reporters observed these monitoring events and provided 
press coverage of the volunteers working alongside the survey crews. 

Volunteer monitors are important partners in the assessment and protection of the nation's lakes, and 
state agencies and EPA should continue to explore pathways for improved communication and cooperation 
with volunteer programs in future surveys of the nation's lakes. 




A volunteer with the Michigan Cooperative 
Lakes Monitoring Program collects a water 
sample for chlorophyll analysis. 

Photo courtesy of Ralph Bednarz. 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 












CHAPTER 6 


ECOREGIONAL RESULTS 




► Southern 
Appalachians 

► Coastal Plains 


► Upper Midwest 

► Temperate Plains 

► Southern Plains 

► Northern Plains 

► Western Mountains 

► Xeric 











Chapter 6 


Ecoregional Results 


Chapter 6 

Ecoregional Results 

Taken individually, each lake is a reflection 
of its watershed. The characteristics of the 
watershed, i.e., its size relative to the lake, 
topography, geology, soil type, land cover, 
and human activities, together influence 
the amount and nature of material entering 
the lake. For example, a deep alpine lake 
located in a Rocky Mountain watershed will 
likely have clear, pristine water and little 
biological productivity. Conversely, a lake in a 
coastal plains watershed of the mid-Atlantic 
region, an area of nutrient-rich alluvial soils 
and a long history of human settlement, 
will more likely be characterized by high 
turbidity, high concentrations of nutrients and 
organic matter, prevalent algal blooms, and 
abundant aquatic weeds and other plants. 
Atmospheric deposition of airborne pollutants, 
as well as nutrients traveling in groundwater 
from hundreds of miles away, can affect the 
watershed and influence the lake condition. 


Lakes in high population areas are 
especially vulnerable. Combined sewer 
overflow and stormwater runoff can carry 
marked amounts of pollutants such as metals, 
excess sediment, bacteria, and most recently, 
pharmaceuticals. As a result, expectations 
and lake condition vary across the country. 

Because of the diversity in landscape, it is 
important to assess waterbodies in their own 
geographical setting. The NLA was designed 
to report findings on an ecoregional scale. 
Ecoregions are areas that contain similar 
environmental characteristics and are defined 
by common natural characteristics such as 
climate, vegetation, soil type, and geology. 

By looking at lake conditions in these smaller 
ecoregions, decision-makers can begin to 
understand patterns based on landform and 
geography, and whether the problems are 
isolated in one or two adjacent regions or are 
widespread. 



IBS®*.? 

r 

A' s-w.%. 

.Vft 

V 

/ 


/ 

-j & 

/ Hr 

mm / 

F 117 

fix#/ 

M\ 

\ 

/ 

ijSr \ 

\ 

\ 

i 


\ P 

if* 

\ .! 


\} 




\ 

! 

■ 

i 

■—k 



NLA Analysis Regions* 

□ NAP 

1 1 SPL 

□ SAP 

1 1 NPL 

r~i cpl 

1 1 XER 

1 1 TPL 

□ UMW 

I 1 WMT 

'based on Omem* Level III erxregons 






Figure 20. Ecoregions used as part of the National Lakes Assessment. 


48 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 





















Chapter 6 


Ecoregional Results 


Biological Condition - Planktonic O/E 



W< 20% Taxa Loss [ 1 20-40% Taxa Loss ^> 40% TaxjT Loss 


Figure 21. Biological condition (based on planktonic O/E taxa loss) across nine ecoregions. 


EPA has defined ecoregions 
at various scales, ranging from 
coarse ecoregions at the continental 
scale (Level I) to finer ecoregions 
that divide the land into smaller 
units (Level III or IV). The nine 
ecoregions used in this assessment 
are aggregations of the Level III 
ecoregions delineated by EPA for 
the continental U.S. These nine 
ecoregions as shown in Figure 20 
are: 

• Northern Appalachians (NAP) 

• Southern Appalachians (SAP) 

• Coastal Plains (CPL) 

• Upper Midwest (UMW) 

• Temperate Plains (TPL) 

• Southern Plains (SPL) 

• Northern Plains (NPL) 

• Western Mountains (WMT) 

• Xeric (XER) 

To assess waters within each ecoregion, 
the NLA captures the geographic variation 
in lakes using regionally-specific reference 
conditions. The resulting set of reference 
lakes all share common characteristics and 
occur within a common geographic area. 5 This 
approach not only allows lakes in one region 
to be compared with the particular reference 
lakes of that region, but also allows for the 
comparison of one ecoregion to another. This 
means that lakes in the arid west are not 
being assessed against lakes in the Southern 
Plains. Yet, at the same time, this also means 
that if 10% of the Xeric west lakes were in 
poor condition and 20% of the Southern 
Plains lakes were relatively poor, one can 
compare the two ecoregions and say that the 
Southern Plains have twice the proportion of 
lakes in poor condition. 


Nationwide Comparisons 

Biological Condition - Taxa Loss 

Regionally, the proportion of lakes with 
good biological condition ranges from 91% in 
the Upper Midwest to < 5% in the Northern 
Plains (Figure 21). In general, the glaciated 
and/or mountainous regions have the highest 
proportion of lakes exhibiting good biological 
condition, followed by Coastal Plains lakes. 

The Xeric west and Northern Plains exhibit the 
highest proportions of lakes in poor condition 
biologically. Forty nine percent of lakes are in 
poor biological condition in the Xeric region, 
while just under 85% of Northern Plains lakes 
are in poor biological condition. 


5 It is important to note that the geographic boundaries of the regionally-specific reference areas do not specifically match those of the nine 
ecoregions. More detailed information about how regional reference lakes were determined can be found in the Technical Report. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


49 




























Chapter 6 


Ecoregional Results 


Lakeshore Habitat 



Western Mountains 


Upper Midwest 


Northern Appalachians 


Northern Plains 


Temperate Plains 


Southern Appalachians ‘ E 


Xeric 


Southern Plains 


Plains 


National 


fGood 


Figure 22. Habitat condition of the nation’s lakes across nine ecoregions based on lakeshore habitat. 


Habitat Stressors - 
Lakeshore Habitat 

In the NLA, habitat stress was assessed 
using four indicators: lakeshore habitat, 
shallow water habitat, physical habitat 
complexity and human disturbance. Of these, 
the most revealing indicator, based on the 
relative and attributable risk analyses, is 
lakeshore habitat. This analysis indicates that 
biological integrity of lakes is three times 
more likely to be poor when the lakeshore 
habitat area is classified as poor. Regionally, 
the proportion of lakes with poor lakeshore 
habitat ranges from a low of 25% in the 
Northern Appalachians to a high of 84% in the 
Northern Plains (Figure 22). Poor lakeshore 
habitat is most prevalent in the Plains and Xeric 
ecoregions. 

Trophic Status 

Regionally, the proportion of lakes 
classified as oligotrophic, based on measures 


of chlorophyll-a, ranges from 54% in the 
Western Mountains to < 5% in the Temperate 
Plains (Figure 23). The highest proportion of 
mesotrophic waters are found in the Northern 
and Southern Appalachians, and the Upper 
Midwest. The proportion of eutrophic lakes is 
highest in the Coastal and Southern Plains. 
Hypereutrophic lakes are most prevalent in the 
Temperate Plains, where nearly 50% of lakes 
are classified hypereutrophic. 

Recreational Suitability - Cyanobacteria 
(blue-green algae) 

Over 75% of lakes in the Western 
Mountains, Xeric west, Upper Midwest, and 
Northern and Southern Appalachians pose 
minimal risk of exposure to cyanobacteria- 
produced toxins. The greatest proportions of 
lakes at high exposure risk (> 100,000 cells/L) 
occur in the Southern, Coastal, and Temperate 
Plains. The Northern Plains have over 50% of 
lakes in the moderate exposure risk category 
(Figure 24). 


so 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 

























Chapter 6 


Ecoregional Results 



Trophic Condition - Chlorophyll a 


itains 


Upper Midwest 


Northern Appalacl 


Northern Plains 


Temperate Plains 


Xeric I 


Southern Plains 


Coastal Plains 


National 


| Oligotrophic Q Mesotrophic r] Eutrophic 

Figure 23. Trophic state across nine ecoregions (based on chlorophyll-aj 


Hypereutrophic 



i Mountains 


Northern Appalachians 


■ Upper Midwest 


Northern Plains 


Southern Appalachians 


Southern Plains 


Coastal Plains 


National 


Moderate Risk | High Risk 


| Low Risk 


Algal Toxin Exposure Risk from Cyanobacteria 


Figure 24. Comparison of exposure to cyanobacteria risk across nine ecoregions. 





National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


■I 











































Chapter 6 


Ecoregional Results 


Northern Appalachians 

The Landscape 

The Northern Appalachians ecoregion 
covers all of the New England states, most of 
New York, the northern half of Pennsylvania, 
and northeast Ohio. It encompasses New 
York's Adirondack and Catskill Mountains and 
Pennsylvania's mid-northern tier, including the 
Allegheny National Forest. Major waterbodies 
include Lakes Ontario and Erie, New York's 
Finger Lakes, and Lake Champlain. There are 
5,226 lakes in the Northern Appalachians that 
are represented by the NLA, 54% of which 
are constructed reservoirs. The ecoregion 
comprises some 139,424 square miles (4.6% 
of the United States), with about 4,722 
square miles (3.4%) under federal ownership. 
Based on satellite images in the National Land 
Cover Dataset (1992), the distribution of 
land cover is 69% forested and 17% planted/ 
cultivated, with the remaining 14% of land in 
other types of cover. 



Dick’s Pond in Massachusetts. 

Photo courtesy of USEPA Region 1. 


Many lakes in the region were created 
for the purpose of powering sawmills. During 
the 18th and early 19th centuries, lakes were 
affected by sedimentation caused by logging, 
farming, and damming of waterways. When 
agriculture moved west and much of eastern 
farmland converted back into woodlands, 
sediment yields declined in some areas. In 
many instances, lakes in what appears to 
be pristine forested settings are in fact still 
recovering from prior land use disturbances. 
In the mountainous regions of the Northern 
Appalachian ecoregion, many large reservoirs 
were constructed throughout the early 20th 
century for hydropower generation and/or 
flood control. 


the ecoregion. An overview of the NLA 
findings for Northern Appalachian lakes is 
shown in Figure 25. 

Biological Condition 

Fifty-five percent of lakes are in good 
biological condition based on planktonic 
O/E, and when using the diatom IBI, 67% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 15% and 10% based on the two 
analyses, respectively. 

Trophic Status 


Findings 


A total of 93 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 


Based on chlorophyll-a, 26% of lakes 
are oligotrophic, 54% are mesotrophic, 17% 
are eutrophic, and only 3% are considered 
hypereutrophic. 


52 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 














Chapter 6 


Ecoregional Results 



Northern Appalachians 
5,226 Lakes 



Diatom IBI 

67 4% 


i 23 0% 




I 9,6% 

Trophic State - Chlorophyll a 

26,3% 

H 53.8% 


0 20 40 60 80 100 0 20 40 60 80 100 

Percentage of Lakes Pe rcentage of Lakes 

For Lake Origin: Low Risk 

Natural MMI Man-Made l ..I Moderate Risk 

For Plankton O/E ES3 High Risk 

i km < 20% Taxa Loss 
!!■ -«« > 40% Taxa Loss 
For Diatom IBI: 

■Hi GoodC 



Absent 

Present 


0 20 40 60 80 100 

Perce ntag e of Lakes 

njEsJ Good 
Fair 
Poor 


□ 20-40% Taxa Loss 


□ Fair 


Poor 


For Trophic State - Chlorophyll a 

Oligotrophi a i Mesotrophic 
i I Eutrophic ESS Hypereutrophic 


Dissolved Oxygen 


93.2% 


Lakeshore Disturbance 

i 42.2% 

-|42 9% 

Lakeshore Habitat 

165.9% 



20 40 60 80 100 

Perce ntag e of Lakes 

MM Good 

I-1 Fair 

i -.TtiLi Poor 


Figure 25. NLA results for the Northern Appalachians. Bars show the percentage of lakes within a condition class for a given indicator. 

For Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated 
with the presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria per se. 


Recreational Suitability 

Using the indicators and World Health 
Organization guidelines described in Chapter 
3, most lakes in the Northern Appalachian 
ecoregion exhibit relatively low risk of 
exposure to cyanobacteria and associated 
cyanotoxins. Based on cyanobacterial counts, 
95% of lakes exhibit low exposure risk. 
Microcystin was present in 9% of lakes. 

Physical Habitat Stressors 

Lakeshore habitat is considered good in 
66% of the lakes in this ecoregion. Given 
the long history of land use and settlement 
in this ecoregion, the shorelines of Northern 
Appalachian lakes exhibit relatively disturbed 


conditions due to human activities. Fifty- 
seven percent of lakes show moderate to high 
levels of lakeshore disturbance. 

Chemical Stressors 

In contrast to physical habitat conditions, 
the majority of Northern Appalachian lakes 
exhibit high-quality waters based on the 
NLA chemical stressor indicators. Relative to 
regionally-specific reference expectations, 
total phosphorus and nitrogen, chlorophyll-a, 
and turbidity levels are considered good in 
80% or more of lakes in this ecoregion. Lakes 
are in good condition based on ANC and 
surface water DO levels when compared to 
nationally-consistent thresholds. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


S3 






















































































Chapter 6 


Ecoregional Results 


Southern Appalachians 

The Landscape 

The Southern Appalachians ecoregion 
stretches over 10 states, from northeastern 
Alabama to central Pennsylvania. Also 
included in this region are the interior 
highlands of the Ozark Plateau and the 
Ouachita Mountains in Arkansas, Missouri, 
and Oklahoma. The region covers about 
321,900 square miles (10.7% of the 
United States) with about 42,210 square 
miles (10.7%) under federal ownership. 

Many important public lands such as the 
Great Smoky Mountains National Park and 
surrounding national forests, the Delaware 
Water Gap National Recreation Area, 
the George Washington and Monongahela 
National Forests, and the Shenandoah 
National Park are located within the region. 
Topography is mostly hills and low mountains 
with some wide valleys and irregular plains. 
Piedmont areas are included within the 
Southern Appalachians ecoregion. 

Natural lakes are nearly non-existent 
in this ecoregion. The 4,690 lakes in the 
Southern Appalachians ecoregion represented 
by the NLA are all man-made. The 
configuration of the Southern Appalachian 
valleys has proven ideal for the construction 
of man-made lakes, and some of the nation's 
largest hydro-power developments can be 
found in the Tennessee Valley. 

Findings 



Pennsylvania lake. 

Photo courtesy of Frank Borsuk. 


Biological Condition 

Forty-two percent of lakes are in good 
biological condition based on planktonic 
O/E and when using the diatom IBI, 63% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 31% and 13% based on the 
two analyses, respectively. The apparent 
difference between these two biological 
indices may suggest that the two indicators 
are responding to different stressors in lakes 
in this particular ecoregion. 

Trophic Status 

Based on chlorophyll-a, 12% of lakes 
are oligotrophic, 46% are mesotrophic, 

17% are eutrophic, and 26% are considered 
hypereutrophic. 


A total of 116 of the selected NLA 
sites were sampled during the summer of 
2007 to characterize the condition of lakes 
throughout the ecoregion. An overview of 
the NLA findings for lakes in the Southern 
Appalachians is shown in Figure 26. 


Recreational Suitability 

While many lakes in the Southern 
Appalachians ecoregion exhibit relatively 
low risk of exposure to cyanobacteria and 
associated cyanotoxins, a quarter of lakes 
exhibit moderate risk levels based on 
chlorophyll-a and cyanobacteria values. 
Microcystin was present in 25% of lakes. 


54 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 







Chapter 6 


Ecoregional Results 






Lake Origin 

100% 


Planktonic O/E 

41.7% 



113.3% 

Trophic State - Chlorophyll a 

( 12 % 

' H45.8% 



Recreational Chlorophyll Risk 

*58 4% 

| 24.5% 


Southern Appalachians 



1 - 1 - 1 -1- -1-1-1-r 

0 20 40 60 80 100 0 20 40 60 80 100 

Percentage of Lakes percentage of Lakes 

For L ake Origin: 

■M Natural 


Total P hosphorus 

1 66.4% 


Tota l Nitrogen 

167 8% 



) 18.7% 

Acid Neutralizing Capacity 


100% 

1 

1 

1 

1 

n 



■ Man-Made 

For Plankton O/E 
■■I < 20% Taxa Loss C 
i J > 40% T axa Loss 
For Diatom IBI: 

BH Good i i Fair 
Poor 

For Trophic State - Chlorophytl a 
Oligotrophic (<= 2 ug/L) C 
i i Eutrophic (>7 to 30 mg/L) ■ 


Low Risk 
Moderate Risk 
High Risk 


Present 

Absent 


0 20 40 60 80 100 

Percentage of Lakes 

rm Good 
I I Fair 
i v: :-i Poor 


0 20 40 60 80 100 

Percentage of Lakes 

Good 
LZD Fair 
( ~1 Poor 


20-40% Taxa Loss 


□ Not Assessed 


Mesotrophic (>2-7 ug/L) 
Hypereutrophic (> 30 ug/L) 


Figure 26. NLA results for the Southern Appalachians. Bars show the percentage of lakes within a condition class for a given indicator. 
For Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated 
with the presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria per se. 


Physical Habitat Stressors 

Lakeshore habitat is considered good in 
42% of the lakes in this ecoregion. Yet the 
shorelines of Southern Appalachians lakes 
indicate considerable lakeshore development 
pressure. Over 90% of lakes show moderate 
to high levels of lakeshore disturbance. 

Chemical Stressors 

Based on the NLA chemical stressor 
indicators, a considerable proportion of 
Southern Appalachians lakes exhibit good 
quality waters. Total phosphorus and nitrogen 
are considered good in 66% and 68% of 
lakes, respectively. Relative to regionally- 


specific reference expectations, chlorophyll-a 
and turbidity levels are considered good 
in 72% or more of the man-made lakes in 
this ecoregion. Man-made lakes are in good 
condition based on ANC and surface water DO 
levels when compared to nationally consistent 
thresholds, although 9% of lakes were ranked 
poor due to low dissolved oxygen. 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 


55 















































































































Chapter 6 


Ecoregional Results 


Coastal Plains 

The Landscape 

The Coastal Plains ecoregion covers the 
Mississippi Delta and Gulf Coast, north along 
the Mississippi River to the Ohio River, all 
of Florida, eastern Texas, and the Atlantic 
seaboard from Florida to New Jersey. Total 
area is about 395,000 square miles (13% of 
the United States) with 25,890 square miles 
(6.6%) under federal ownership. Based on 
satellite images in the 1992 National Land 
Cover Dataset, the distribution of land cover 
is 39% forested, 30% planted/cultivated, 
and 16% wetlands, with the remaining 15% 
of land in other types of cover. Damming, 
impounding, and channelization in this 
ecoregion have altered the rate and timing of 
water flow and delivery to lakes. 

A subset of major lakes of the region 
includes the Toledo Bend (TX) and 
Sam Rayburn Reservoirs (TX/LA), Lake 
Okeechobee (FL), Lake Marion (SC), and 
the massive lake-wetland complexes north 
of the Gulf Coast. The Coastal Plains is also 
home to a variety of lakes and ponds, such 
as Cape Cod kettleholes, New Jersey Pine 
Barren ponds, southeastern blackwater lakes, 
Carolina "Bays," and the limestone-rich clear 
lakes of the Florida peninsula. A total of 7,009 
lakes and reservoirs in the Coastal Plains 
ecoregion are represented in the NLA, and 
69% of these are man-made. 

Findings 

A total of 102 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 
the ecoregion. An overview of the NLA 
findings for the Coastal Plains lakes is shown 
in Figure 27. 



Biological Condition 

Forty-seven percent of lakes are in good 
biological condition based on planktonic 
O/E, and when using the diatom IBI, 57% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 27% and 6% based on the two 
analyses, respectively 

Trophic Status 

Based on chlorophyll-a, 6% of the lakes 
are mesotrophic, 60% are eutrophic, and 
34% are considered hypereutrophic. 

Recreational Suitability 

Lakes in the Coastal Plains ecoregion 
exhibit moderate risk of exposure to 
cyanobacteria and associated cyanotoxins. 
Based on cyanobacterial counts, 64% of lakes 
exhibited low exposure risk. Microcystin was 
present in 35% of lakes. 


56 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 











Chapter 6 


Ecoregional Results 



s“ 


Recreational Chlorophyll Risk 

11.5% 


Coastal Plains 
7,009 Lakes 


-162.2% 


26.3% 

Cyanobacteria Risk 

64 1% 



Trophic State - Chlorophyll a 

5.5% 

160 0% 



Microcystin Presence 

\ 65.4% 




15.3% 


Total Phosphorus 

477% 


Total Nitrogen 

50 9% 

145 6% 

Chlorophyll 

■I 65% 


- I 



Turbidity 


Acid Neutralizing Capacity 


0 20 40 60 80 100 

Percentage of Lakes 

For Lake Origin: 

■■ Natural ■■ Man-Made 
For Plankton O/E 
■BB < 20% Taxa LossC 
i i > 40% Taxa Loss 
For Diatom IBI: 

BBS Good[ 


t -r 

0 20 40 60 80 100 

Percentage of Lakes 

EEZD Low Risk r—~i Present 
I I Moderate Risk i 7 ^ Absent 
High Risk 
20-40% Taxa Loss 


97.6% 1 

]-| 2.4% 






Dissolved Oxygen 

165 7% 


I—| —112 5% 

- | 0.5% 

]-| 2.5% 

- 1 - 118 . 8 % 


Lakeshore Disturbance 

I 16.4% 


I 64 6% 



t -r~ 

0 20 40 60 80 100 0 20 40 60 80 100 

Percentage of Lakes Percentage of Lakes 

k .'V 7 Good Good 

I-1 Fair dZ] Fair 

i :,d Poor da Poor 

Not Assessed 
No Data 


Fair I 


Poor 


For Trophic State - Chlorophyll a 
BBi Oligotrophic (<= 2 ug/L) C 


Mesotrophic (>2-7 ug/L) 


Figure 27. NLA findings for the Coastal Plains. Bars show the percentage of lakes within a condition class for a given indicator. For 
Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated 
with the presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria perse. 


Physical Habitat Stressors 

Lakeshore habitat is considered good in 
22% of the lakes in this ecoregion. Moreover, 
the shorelines of the Coastal Plains lakes 
are highly disturbed, indicating considerable 
lakeshore development pressure in this 
region. About 84% of lakes show moderate to 
high levels of lakeshore human disturbance. 

Chemical Stressors 


51% of lakes, respectively, and are poor in 
15% and 4% of lakes, respectively. Relative 
to regionally-specific reference expectations, 
chlorophyll-a concentrations are considered 
good in 65% of lakes, and turbidity levels 
are considered good in 85% of lakes in this 
ecoregion. Lakes are in good condition based 
on ANC and surface water DO levels when 
compared to nationally-consistent thresholds, 
although 13% of lakes were ranked fair due 
to low dissolved oxygen. 


Based on the NLA chemical stressor 
indicators, water quality is somewhat variable 
across the Coastal Plains. Total phosphorus 
and nitrogen are considered good in 48% and 


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57 








































































































Chapter 6 


Ecoregional Results 


Upper Midwest 

The Landscape 

The Upper Midwest ecoregion covers 
most of the northern half and southeastern 
part of Minnesota, two-thirds of Wisconsin, 
and almost all of Michigan, extending about 
160,374 square miles (5.4% of the United 
States). A total of 15,562 lakes in the 
ecoregion are represented in the NLA, nearly 
all of which are of natural origin, reflecting 
the glaciation history of this region. Sandy 
soils dominate with relatively high water 
quality in lakes supporting warm and cold- 
water fish communities. Major lakes of the 
region include the Great Lakes (which, for 
design considerations, were not represented 
by the NLA), and also Lake of the Woods 
and Red Lake (MN). The glaciated terrain of 
this ecoregion is typically plains with some 
hill formations. The northern tier of this 
ecoregion has a very high number of smaller 
lakes, both drainage and seepage, which 
range widely in geochemical makeup. Much 
of the land is covered by national and state 
forest. Federal lands account for 15.5% of 
the area at about 25,000 square miles. Based 
on satellite images in the 1992 National Land 
Cover Dataset, the distribution of land cover 
is 40% forested, 34% planted/cultivated, 
and 17% wetlands, with the remaining 9% 
of land in other types of cover. Most of the 
landscape was influenced by early logging and 
agricultural activities. 

Findings 

A total of 148 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 
the ecoregion. An overview of the NLA 
findings for the Upper Midwest lakes is shown 
in Figure 28. 



Minnesota prairie pothole lake. 

Photo courtesy of Steve Heiskary. 


Biological Condition 

Ninety-one percent of lakes are in good 
biological condition based on planktonic 
O/E, and when using the diatom IBI, 47% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 4% and 22% based on the two 
analyses, respectively. The difference between 
these two biological indices may suggest that 
the two indicators are responding to different 
stressors in lakes in this particular ecoregion. 

Trophic Status 

Based on chlorophyll-a, 9% of lakes are 
oligotrophic, 54% are mesotrophic, 26% 
are eutrophic, and 10% are considered 
hypereutrophic. 


58 


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Chapter 6 


Ecoregional Results 



Upper Midwest 
15,562 Lakes 





Lake Origin 

97.3% 

L 2.7% 


Planktonic O/E 

91.2% 



Diatom IBI 

46.8% 


22 . 0 % 

State - Chlorophyll a 


I- 

-125 7% 

98% 


I-1 -154 2% 


i -1-r 


Recreational Chlorophyll Risk 



Microcystin Presence 

H76 8% 



99 . 1 % ; 

- 1 0.9% 






Shallow Water Habitat 

58.5% 


Physical Hab itat Complexity 

-150 3% 



24.1% 

|25.3% 


Absent 


0 20 40 60 80 100 0 20 40 60 80 100 0 

Percentage of Lakes Percentage of Lakes 

For L ake Origin:_ i .t Low Risk i: ' i Present 

■■ Natural MM Man-Made 

For Plankton O/E 

< 20% Taxa LossC 
i i > 40% Taxa Loss 
For Diatom IBI: 
r&AS* Good C 


Moderate Risk 

■■ High Risk 
20-40% Taxa Loss 


20 40 60 80 100 

Percentage of Lakes 

i-'.L/J Good 

I-1 Fair 

Poor 


-i-1-1-1- 

0 20 40 60 80 100 

Percentage of Lakes 

ESSSl Good 
i i Fair 

1 1 Poor 


Fair | 


Poor 


For Trophic State - Chlorophyll a 
iR-stsa Oligotrophic (<= 2 ug/L) C 
Eutrophic (>7 to 30 mg/L) I 


Mesotrophic (>2-7 ug/L) 
Hypereutrophic (> 30 ug/L) 


Figure 28. NLA findings for the Upper Midwest. Bars show the percentage of lakes within a condition class for a given indicator. For 
Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated 
with the presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria per se. 


Recreational Suitability 

Lakes in the Upper Midwest exhibit 
relatively low risk of exposure to 
cyanobacteria and associated cyanotoxins. 
Based on cyanobacterial counts, 81% of lakes 
exhibited low exposure risk. Microcystin was 
present in 23% of lakes. 

Physical Habitat Stressors 

Lakeshore habitat is considered good 
in 54% of the lakes in this ecoregion. The 
shorelines of the Upper Midwest lakes, 
indicate considerable lakeshore development 
pressure. Forty-six percent of lakes show 
moderate to high levels of lakeshore human 
disturbance. 


Chemical Stressors 

Based on the NLA chemical stressor 
indicators, water quality is relatively good 
across the Upper Midwest. Total phosphorus 
and nitrogen are considered good in 66% and 
59% of lakes, respectively, and are poor in 
9% and 8%, of lakes respectively. Relative 
to regionally-specific reference expectations, 
chlorophyll-a concentrations are considered 
good in 68% of lakes, and turbidity levels 
are considered good in 77% of lakes in this 
ecoregion. Lakes are in good condition based 
on ANC and surface water DO levels when 
compared to nationally-consistent thresholds. 


National Lakes Assessment: A Collaborative Survey of the Nations Lakes 


59 
























































































Chapter 6 


Ecoregional Results 


Temperate Plains 

The Landscape 

The Temperate Plains ecoregion includes 
the open farmlands of Iowa; eastern North 
and South Dakota; western Minnesota; 
portions of Missouri, Kansas, and Nebraska; 
and the flat farmlands of western Ohio, 
central Indiana, Illinois, and southeastern 
Wisconsin. This ecoregion covers some 
342,200 square miles (11.4% of the United 
States), with approximately 7,900 square 
miles (2.3%) in federal ownership. The terrain 
consists of smooth plains, numerous small 
lakes, prairie pothole lakes, and wetlands. A 
total of 6,327 lakes in the Temperate Plains 
ecoregion are represented in the NLA, of 
which 75% are of natural origin. Lakes of 
this region are generally small, with over 
60% of lakes smaller than 100 hectares in 
size. Agriculture is the predominant land 
use. Based on satellite images in the 1992 
National Land Cover Dataset, the distribution 
of land cover is 9% forested and 76% 
planted/cultivated, with the remaining 15% of 
land in other types of cover. 

Findings 

A total of 137 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 
this ecoregion. An overview of the NLA 
findings for the Temperate Plains lakes is 
shown in Figure 29. 

Biological Condition 

One quarter, or 24%, of lakes are in 
good biological condition based on planktonic 
O/E, and when using the diatom IBI, 17% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 35% and 52% based on the two 
analyses, respectively. 


Sampling with a D-net for benthic macroinvertebrates. 

Photo courtesy of Great Lakes Environmental Center. 


Trophic Status 

Based on chlorophyll-a, 2% of lakes are 
oligotrophic, 32% are mesotrophic, 21% 
are eutrophic, and 45% are considered 
hypereutrophic. 

Recreational Suitability 

Lakes in the Temperate Plains exhibit 
moderate risk of exposure to cyanobacteria 
and associated cyanotoxins. Based on 
cyanobacterial counts, 48% of lakes exhibited 
low exposure risk. Microcystin was present in 
67% of lakes. 



60 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 









Chapter 6 


Ecoregional Results 



Acid Neutralizing Capacity 


100 % 

1 

1 


1 

1 



0 20 40 60 80 100 0 20 40 60 80 100 0 

Percentage of Lakes Percentage of La kes 

For Lake Origin: l i Low Risk 1— ' - - l Present 

ESS Natural HBI Man-Made I I Moderate Risl^H Absent 

For Plankton O/E t-TI • I High Risk 

ES33 < 20% Taxa Loss I I 20-40% Taxa Loss 

l. , :-a > 40% Taxa Loss 

For Diatom IBI: 

MB Good I I Fair I - I Poor 


20 40 60 80 

Percentage of Lakes 

tatea Good 

I-1 Fair 

I_I Poor 


100 0 20 40 60 80 100 

Percentage of Lakes 

t /■-•)! Good 
dZJ Fair 
r i Poor 


For Trophic State - Chlorophyll a 
rr~"~l Ollgotrophic (<= 2 ug/L) 

i i Eutrophic (>7 to 30 mg/L) 


Mesotrophic (>2-7 ug/L) 
Hypereutrophlc (> 30 ug/L) 


Figure 29. NLA findings for the Temperate Plains. Bars show the percentage of lakes within a condition class for a given indicator. For 
Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated 
with the presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria per se. 


Physical Habitat Stressors 

Lakeshore habitat is considered good 
in 56% of the lakes in this ecoregion. The 
shorelines of the Temperate Plains lakes 
exhibit human activity disturbances, urban 
development, and agricultural pressures 
in this region. Sixty percent of lakes show 
moderate to high levels of lakeshore human 
disturbance. 

Chemical Stressors 

Based on the NLA chemical stressor 
indicators, water quality in the Temperate 
Plains is somewhat variable. Total phosphorus 


and nitrogen are considered good in 38% and 
27% of lakes, respectively, and are poor in 
30% and 40% of lakes, respectively. Relative 
to regionally-specific reference expectations, 
chlorophyll-a concentrations are considered 
good in 56% of lakes, and turbidity levels 
are considered good in 84% of lakes in 
this ecoregion. Lakes are generally in good 
condition based on ANC and surface water DO 
levels when compared to nationally-consistent 
thresholds. However, dissolved oxygen is fair 
in 12% of lakes. 


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61 


































































































Chapter 6 


Ecoregional Results 


Southern Plains 

The Landscape 

The Southern Plains ecoregion covers 
approximately 405,000 square miles (13.5% 
of the United States) and includes central 
and northern Texas; most of western 
Kansas and Oklahoma; and portions of 
Nebraska, Colorado, and New Mexico. The 
terrain is a mix of smooth and irregular 
plains interspersed with tablelands and low 
hills. Most of the great Ogallala aquifer lies 
underneath this region. 

Based on satellite images in the 1992 
National Land Cover Dataset, the distribution 
of land cover is 45% grassland, 32% planted/ 
cultivated, and 14% shrubland, with the 
remaining 9% of land in other types of 
cover. The Great Prairie grasslands, which 
once covered much of the Southern Plains 
region, are considered the most altered and 
endangered large ecosystem in the United 
States. About 90% of the original tall grass 
prairie has been replaced by other vegetation 
or land use. Federal land ownership in the 
region totals about 11,980 square miles or 
approximately 3% of the total, the lowest 
share of all NLA aggregate ecoregions. A 
total of 3,148 lakes in the Southern Plains 
ecoregion are represented in the NLA, 97% of 
which are constructed reservoirs. 

Findings 

A total of 128 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 
this ecoregion. An overview of the NLA 
findings for the Southern Plains lakes is 
shown in Figure 30. 



Comanche Creek Reservoir. 

Photo courtesy of Texas Commission of Environmental Quality. 


Biological Condition 

Thirty-four percent of lakes are in good 
biological condition based on planktonic 
O/E, and when using the diatom IBI, 41% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 29% and 23% based on the two 
analyses, respectively. 

Trophic Status 

Based on chlorophyll-a, 9% of lakes are 
oligotrophic, 14% are mesotrophic, 51% 
are eutrophic, and 26% are considered 
hypereutrophic. 

Recreational Suitability 

Lakes in the Southern Plains exhibit 
moderate risk of exposure to cyanobacteria 
and associated cyanotoxins. Based on 
cyanobacterial counts, 57% of lakes exhibit 
low exposure risk. Microcystin was present in 
21% of lakes. 


62 


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Chapter 6 


Ecoregional Results 






96.7% 


Southern Plains 
3,148 Lakes 


1 ^ 33 % 


Lake Origin 


Planktonic O/E 

| 34.0% 

H 36% 


I 29 4% 


Diatom IBI 


40 7% 


32.2% 


- Chlorophyll a 


26 1% 




Total Phosphorus) 


72.7% 


|20 1% 


Total Nitrogen 

155.3% 


Chlorophyll 


82 . 1 % 




100% 

1 

1 

1 

1 



t -1-1-r 


Dissolved Oxygen 




Lakeshore Disturbance 

19.3% 

598% 


Lakeshore Habitat 

136 8 % 


| 40.5% 


Shallow Water Habitat 


57 6% 


Physical Habitat Complexity 

41 5% 


0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 


Percentage of Lakes 

Percentage of Lakes 

Percentage of Lakes 

Percentage of Lakes 

For Lake Origin: 

t:. i Low Risk i .r ~i Present 

Good 

fead Good 

■■i Natural ■■ Man-Made 

1 1 Moderate Risk ■■■ Ahsfint 

1_1 Fair 

1_1 Fair 

For Plankton O/E I — . 1 High Risk 

■■B < 20% Taxa Lossi 1 20-40% Taxa Loss 

> 40% T axa Loss 

tagJt Poor 

rm Poor 


For Diatom IBI: 
■■ Goodl 


Fair! 


Poor 


For Trophic State - Chlorophyll a 
H Oligotrophic (<= 2 ug/L) L 
i I Eutrophic (>7 to 30 mg/L) ■ 


Mesotrophic (>2-7 ug/L) 
Hypereutrophic (> 30 ug/L) 


Figure 30. NLA findings for the Southern Plains. Bars show the percentage of lakes within a condition class for a given indicator. For 
Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated 
with the presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria perse. 


Physical Habitat Stressors 

Lakeshore habitat is fair to poor in 63% 
of the lakes in this ecoregion. The shorelines 
of Southern Plains lakes exhibit considerable 
disturbed conditions due to human activities. 
Ninety percent of lakes show moderate to 
high levels of lakeshore human disturbance. 


chlorophyll-a concentrations and turbidity 
levels are considered good in over 80% of 
lakes in this ecoregion. Lakes are generally 
in good condition based on ANC and surface 
water DO levels when compared to nationally- 
consistent thresholds. However, dissolved 
oxygen is fair in 12% of lakes. 


Chemical Stressors 


Water quality, based on the NLA chemical 
stressor indicators, is relatively good in 
the Southern Plains. Total phosphorus and 
nitrogen are considered good in 73% and 
55% of lakes, respectively, and are poor in 
7% and 20% of lakes, respectively. Relative 
to regionally-specific reference expectations, 



National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 


63 































































































Chapter 6 


Ecoregional Results 


Northern Plains 

The Landscape 

The Northern Plains ecoregion covers 
approximately 205,084 square miles (6.8% 
of the United States), including western 
North and South Dakota, Montana east of the 
Rocky Mountains, northeast Wyoming, and a 
small section of northern Nebraska. Federal 
lands account for 52,660 square miles or 
a relatively large 25.7% share of the total 
area. Terrain of the area is irregular plains 
interspersed with tablelands and low hills. 

This ecoregion is the heart of the Missouri 
River system and is almost exclusively within 
the Missouri River's regional watershed. 
Several major reservoirs are along the 
Missouri River mainstem, including Lake Oahe 
and Lake Sacajawea. The total surface area 
of lakes in this region is growing owing to 
increased runoff coupled with flat topography. 
Devil's Lake (ND) is one example, which in 
1993 had a surface area of 44,000 acres and 
presently covers in excess of 130,000 acres. 

Based on satellite images in the 1992 
National Land Cover Dataset, the distribution 
of land cover is 56% grassland and 30% 
planted/cultivated, with the remaining 14% 
of land in other types of cover. A total of 
2,660 lakes in the Northern Plains ecoregion 
are represented in the NLA, 77% of which are 
of natural origin. 

Findings 

A total of 65 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 
this ecoregion. An overview of the NLA 
findings for the Northern Plains ecoregion is 
shown in Figure 31. 



A Northern Plains lake. 

Photo courtesy of Tetra Tech. 


Biological Condition 

The Northern Plains has the highest 
proportion of lakes in poor biological condition 
of any of the ecoregions. Ninety percent of 
lakes are in poor biological condition based 
on planktonic O/E, and 88% are in poor 
condition based on the diatom IBI. 

Trophic Status 

Based on chlorophyll-a, 8% of lakes are 
oligotrophic, 22% are mesotrophic, 48% 
are eutrophic, and 22% are considered 
hypereutrophic. 

Recreational Suitability 

Lakes in the Northern Plains exhibit the 
greatest risk of exposure to cyanobacteria 
and associated cyanotoxins of all ecoregions. 
Based on cyanobacterial counts, 59% of 
lakes exhibit moderate to high exposure risk. 
Microcystin was present in 75% of lakes. 

Physical Habitat Stressors 

Lakeshore habitat cover is considered 
good in only 7% of the lakes in this 
ecoregion. Regionally-specific habitat 
reference condition for the Northern Plains 


64 


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Chapter 6 


Ecoregional Results 




Recreational Chlorophyll Risk 

i-132.3% 


Northern Plains 
2,660 Lakes 


I | -1 53 0% 


14.6% 



26.8% 

Planktonic O/E 




Trophic State - Chlorophyll a 

7.7% 

I-1 -1 22 4% 


Cyanobacteria Risk 

- 140 . 6 % 

I- ' | -150 4% 


6 0 % 


Microcystln Risk 




0.7% 

2 . 2 % 


Microcystin Presence 

125.3% 



1 F— 3 ■ 

Total 

!2.0% 

—1 6 9% 




Acid Neutralizing Capacity 


H 48.2% 


0 20 40 60 80 100 0 20 40 60 80 100 

Percentage of Lakes Percentage of Lakes 

For Lake Origin: i«gw Low Risk i -i Present 

Natural ■■ Man-Made I i Moderate Risk Hi Absent 

For Plankton O/E i • a High Risk 

■I < 20% Taxa Loss I I 20-40% Taxa Loss 
■■H > 40% Taxa Loss 
For Diatom IBI: 

■Hi Good C 


100% 

1 

1 

1 

1 

; 


Dissolved Oxygen 


-3H4,5% 

10.7% 


Lakeshore Disturbance 


0 3% 




H64.4% 


35.1% 


£ 


Lakeshore Habitat 


7 1% 
7 8% 



Shallow Water Habitat 

-1 47 4% 


120 . 1 % 



H31 7% 


Physical Habitat Complexity 

9 6% 



0 20 40 60 80 100 

Percentage of Lakes 

ceami Good 
CZZ) Fair 
r~- I Poor 


H57 9°/i 


0 20 40 60 80 100 

Percentage of Lakes 

s-’- l Good 
I I Fair 
Poor 


□ Fair 


Poor 


For Trophic State - Chlorophyll a 
BBS Oligotrophic (<= 2 ug/L) 
Eutrophic (>7 to 30 mg/L) 


Mesotrophic (>2-7 ug/L) 
Hypereutrophic (> 30 ug/L) 


Figure 31. NLA findings for the Northern Plains. Bars show the percentage of lakes within a condition class for a given indicator. For 
Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated 
with the presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria perse. 


is comprised of grasses and shrubs and is 
different from many of the other ecoregions 
where expectations include a tree layer in 
addition to a middle and lower story. Even 
taking into account the regional-specific 
expectations, the NLA data show that the 
Northern Plains lake shorelines exhibit very 
high levels of disturbance due to human 
activities. Ninety-nine percent of lakes show 
moderate or high levels of lakeshore human 
disturbance. 

Chemical Stressors 

Based on the NLA chemical stressor 
indicators, water quality is variable in 
the Northern Plains. In general, lakes in 
this ecoregion tend to have high levels of 


nutrients. Relative to regionally-specific 
reference expectations, total phosphorus 
concentrations are considered poor in 71% of 
lakes, while total nitrogen concentrations are 
considered poor in 91% of lakes. By contrast, 
based on chlorophyll-a, 78% of lakes are 
considered in good condition, and turbidity 
levels are good in 70% of lakes. 

In the Northern Plains ecoregion, the 
traditional limnological concept that biomass 
production is controlled simply by nutrient 
concentrations may not apply. Lakes are 
generally in good condition based on ANC and 
surface water DO levels when compared to 
nationally-consistent thresholds. 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 


65 
















































































































Chapter 6 


Ecoregional Results 


Western Mountains 

The Landscape 

The Western Mountains ecoregion 
includes the Cascade, Sierra Nevada, Pacific 
Coast ranges in the coastal states; the Gila 
Mountains in the southwestern states; and 
the Bitterroot and Rocky Mountains in the 
northern and central mountain states. This 
region covers approximately 397,832 square 
miles, with about 297,900 square miles or 
74.8% classified as federal land — the highest 
proportion of federal property among the 
nine aggregate ecoregions. The terrain of this 
area is characterized by extensive mountains 
and plateaus separated by wide valleys and 
lowlands. Lakes in this region, in particular 
those within smaller, high-elevation drainages, 
are very low in nutrients and are very dilute 
in other water chemistry constituents (e.g., 
calcium). Therefore biological productivity 
in these systems is limited in their natural 
condition. Accordingly, these smaller, high 
elevation lakes are very sensitive to effects of 
human disturbances. 

Lakes and ponds of the region range 
from large mainstem impoundments to high- 
mountain caldera and kettle lakes. Most 
famous among these mountain caldera lakes 
are Crater Lake (OR) and Lake Yellowstone 
(WY). The single deepest measurement of 
Secchi disk transparency recorded during 
the NLA - 122 feet (37 meters) - occurred 
in this ecoregion in Waldo Lake (OR). Based 
on satellite images in the 1992 National Land 
Cover Dataset, the distribution of land cover 
is 59% forest, 32% shrubland and grassland 
with the remaining 9% of land in other types 
of cover. A total of 4,122 lakes in the Western 
Mountains ecoregion are represented in the 
NLA, 67% of which are of natural origin. 



Survey crews travel on horseback to reach remote lakes. 

Photo courtesy of Tetra Tech. 


Findings 

A total of 155 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 
this ecoregion. An overview of the NLA 
findings for the Western Mountains lakes is 
shown in Figure 32. 

Biological Condition 

Fifty-eight percent of lakes are in good 
biological condition based on planktonic 
O/E, and when using the diatom IBI, 50% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 11% and 3% based on the two 
analyses, respectively. 

Trophic Status 

Based on chlorophyll-a, 54% of lakes 
are oligotrophic, 26% are mesotrophic, 

16% are eutrophic, and 4% are considered 
hypereutrophic. The Western Mountains 
ecoregion has the highest proportion of 
oligotrophic lakes (very clear with low 
productivity) of any of the ecoregions across 
the country. 


66 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 











Western Mountains 
4,122 Lakes 



Trophic State - Chlorophyll a 

-1 54.3% 



Recreational Chlorophyll Risk 


E 


6 % 

2 % 


Cyanobacteria Risk 


-^4.1% 


Microcystin Risk 

1 100% 


Microcystin Presence 

94.9% 


I 5.1% 


Chapter 6 Ecoregional Results 


Tota l Phosphorus 

156.3% 




Turbidity 

56.0% 


12 . 6 % 

Acid Neutralizing Capacity 


99.9% 

0 .1% 







0 20 40 60 80 100 0 

Percentage of Lakes 

For Lake Origin: 


Natural Man-Made 
For Plankton O/E 

< 20% Taxa LossC 
■M > 40% T axa Loss 
For Diatom IBI: 

■■■ Good I I FairBBH Poor 

For Trophic State - Chlorophyll a 
■H Oligotrophic (<= 2 ug/L) 
r r i Eutrophic (>7 to 30 mg/L) 


20 40 60 80 100 0 20 40 60 80 100 

Percentage of Lakes Percentage of Lakes 

E3KB Low Risk xtm Present E3S Good 

I I Moderate Risk Absent I I Fair 

CT~] Poor 


^■1 High Risk 
20-40% Taxa Loss 


0 20 40 60 80 100 

Percentage of Lakes 

Good 
Fair 
Poor 


Mesotrophic (>2-7 ug/L) 
Hypereutrophic (> 30 ug/L) 


Figure 32. NLA findings for the Western Mountains. Bars show the percentage of lakes within a condition class for a given indicator. For 
Recreational Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated with the 
presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria perse. 



Lakes in the Western Mountains exhibit 
the lowest risk of exposure to cyanobacteria 
and associated cyanotoxins of all ecoregions. 
Based on cyanobacterial counts, 96% of lakes 
exhibit low exposure risk. Microcystin was 
present in only 5% of lakes. 

Physical Habitat Stressors 

Lakeshore habitat is considered good in 
48% of the lakes in this ecoregion. Similar 
to the Northern Plains, regionally-specific 
reference conditions were modified in this 
ecoregion to account for sparse natural 
vegetation cover types expected in this 
mountainous region. With respect to human 
activity along the lakeshore, this ecoregion 
has the lowest percentage of lakes with 
human disturbance of all regions. Forty-three 


percent of lakes show moderate to high levels 
of lakeshore human disturbance. 

Chemical Stressors 

Based on the NLA chemical stressor 
indicators, water quality in the Western 
Mountains is consistently in the medium 
range. Relative to regionally-specific reference 
expectations, total phosphorus concentrations 
are considered good in 56% of lakes, fair 
in 11%, and poor in 33%. Total nitrogen 
concentrations are considered good in 52% 
of lakes, fair in 10%, and poor in 38%. Based 
on chlorophyll-a, 48% of lakes are considered 
in good condition, 17% in fair condition, and 
35% in poor condition. Turbidity levels are 
good in 56% of lakes and fair in 31% of lakes. 
Lakes are in good condition based on ANC and 
surface water DO levels when compared to 
nationally-consistent thresholds. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


67 


















































































Chapter 6 


Ecoregional Results 


Xeric 

The Landscape 

The Xeric ecoregion covers the largest 
area of all NLA aggregate ecoregions. This 
ecoregion covers portions of eleven western 
states and all of Nevada for a total of about 
636,583 square miles (21.2% of the United 
States). Some 453,000 square miles or 
71.2% of the land is classified as federal 
lands, including large tracts such as the 
Grand Canyon National Park (AZ), Big Bend 
National Park (TX), and the Hanford Nuclear 
Reservation (WA). The Xeric ecoregion is 
comprised of a mix of physiographic features. 
The region includes the flat to rolling 
topography of the Columbia/Snake River 
Plateau; the Great Basin; Death Valley; and 
the canyons, cliffs, buttes, and mesas of the 
Colorado Plateau. All of the non-mountainous 
area of California falls in the Xeric ecoregion. 

In southern areas, dry conditions and 
water withdrawals produce internal drainages 
that end in saline lakes or desert basins 
without reaching the ocean. Large lakes in 
the southwestern canyon regions are the 
products of large dam construction projects. 
Water levels in these lakes fluctuate widely 
due to large-scale water removal for cities 
and agriculture. Recently, shifts in climate and 
rainfall patterns have resulted in considerably 
reduced water levels on several of the major 
Colorado River impoundments including Lake 
Mead, Lake Powell, and Lake Havasu. Based 
on satellite images in the 1992 National Land 
Cover Dataset, the distribution of land cover is 
61% shrubland and 15% grassland, with the 
remaining 24% of land in other types of cover. 
A total of 802 lakes in the Xeric ecoregion are 
represented in the NLA, 91% of which are 
constructed reservoirs. 



Lewis Lake, NM. 

Photo courtesy of Tetra Tech. 


Findings 

A total of 84 of the selected NLA sites 
were sampled during the summer of 2007 to 
characterize the condition of lakes throughout 
the ecoregion. An overview of the NLA results 
for the Xeric ecoregion is shown in Figure 33. 

Biological Condition 

Thirty-seven percent of lakes are in good 
biological condition based on planktonic 
O/E, and when using the diatom IBI, 70% of 
lakes in the ecoregion are in good biological 
condition relative to reference condition. 
Conversely, the percentages of lakes in poor 
condition are 49% and 6% based on the two 
analyses, respectively. The difference between 
these two biological indices may suggest that 
the two indicators are responding to different 
stressors in lakes in this particular ecoregion. 

Trophic Status 

Based on chlorophyll-a, 22% of lakes 
are oligotrophic, 27% are mesotrophic, 

22% are eutrophic, and 28% are considered 
hypereutrophic. 



National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 









Chapter 6 


Ecoregional Results 



Recreational Chlorophyll Risk 

H50 9% 




Xeric 
802 Lakes 


8.9% 


Lake Origin 


Planktonic O/E 

35 7% 


49.3% 

Diatom IBI 

70.5% 



i 5.6% 

Trophic State - Chlorophyll i 

H 22.3% 

A.27.3% 


i 

0 20 40 60 80 

Percentage of Lakes 

For Lake Origin: 

BBS Natural BH Man-Made 
For Plankton O/E 
^B < 20% T axa Loss [ 
i- '4 > 40% Taxa Loss 

For Diatom IBI: 

■B Good 




Ota I Phosphorus 

■{44.7% 


Total Nitrogen 

40.2% 

56.7% 


Chlorophyll 

) 50 2% 


Turbidity 

41.4% 

139.1% 

| 19.6% 

Acid Neutralizing Capacity 


100% 

E 

■ 

1 




100 0 


20 40 60 80 100 0 

Percentage of Lakes 

3EJ Low Risk BH Present 
ZH Moderate Risk Absent 

S3 High Risk 


20 40 60 80 100 0 

Percentage of Lakes 

■B Good 
I I Fair 
EEH Poor 


20 40 60 80 100 

Percentage of Lakes 

L--- : L;:l Good 
IZZD Fair 
BaWRI Poor 


] 20-40% Taxa Loss 


Fair 


Poor 


For Trophic State - Chlorophyll a 
it '.1 Oligotrophic (<= 2 ug/L) 

1 I Eutrophic (>7 to 30 mg/L)l 


Mesotrophic (>2-7 ug/L) 
Hypereutrophic (> 30 ug/L) 


Figure 33. NLA findings for the Xeric. Bars show the percentage of lakes within a condition class for a given indicator. For Recreational 
Chlorophyll risk and Cyanobacteria risk, the percentage numbers indicate the risk of exposure to algal toxins associated with the 
presence of cholorphyll-a and cyanobacteria, not the risk of exposure to chlorophyll-a and cyanobacteria perse. 


Recreational Suitability 

Lakes in the Xeric ecoregion exhibit 
low to moderate risk of exposure to 
cyanobacteria and associated cyanotoxins. 
Based on cyanobacterial counts, 82% of 
lakes exhibit low exposure risk. Microcystin 
was present in 23% of lakes. 

Physical Habitat Stressors 

Lakeshore habitat is considered good 
in 34% of the lakes in this ecoregion. In 
the Xeric ecoregion, regionally-specific 
reference conditions were modified to 
account for sparse natural vegetation cover 
types expected in this dry region. Lakes 
in the Xeric ecoregion exhibit considerably 
disturbed conditions due to human activities. 
Over 89% of lakes show moderate to high 
levels of lakeshore human disturbance. 


Chemical Stressors 

Like the Western Mountains ecoregion 
to the north, the water quality in the Xeric 
ecoregion is in the medium range. Relative 
to regionally-specific reference expectations, 
total phosphorus concentrations are 
considered good in 45% of lakes, fair in 
28%, and poor in 28%. Total nitrogen 
concentrations are considered good in 
40% of lakes, fair in 57%, and poor in 
3%. Based on chlorophyll-a, 50% of lakes 
are considered in good condition, 21% in 
fair condition, and 29% in poor condition. 
Turbidity levels are good in 41% of lakes, 
and fair in 39%. Lakes are good condition 
based on ANC and surface water DO levels 
when compared to nationally-consistent 
thresholds. 


/ ; _____ | 69 

National Lakes Assessment: A Collaborative Survey of the Nation's Lakes 





































































































HIGHLIGHT 



Partnerships for a Statewide Assessment 
of Lake Condition 


Steve Heiskary 

Minnesota Pollution Control Agency 


National Lake Assessment Program 
Random and Reference Lake Locations 














& 


« *9» M 10 130 


In 2007, the Minnesota Pollution Control Agency (MPCA) 
along with the Minnesota Department of Natural Resources 
(MDNR) led the State's participation in USEPA's National Lakes 
Assessment survey. Various other collaborators were engaged in 
this study as well, including the U.S. Forest Service (USFS), the 
Minnesota Department of Agriculture (MDA), and U.S. Geological 
Survey (USGS). MPCA and MDNR combined on initial planning 
of the survey and conducted the vast majority of the sampling. 
USFS staff were instrumental in sampling remote lakes in the 
northeastern Boundary Waters Canoe Area Wilderness. 

Minnesota was assigned 41 lakes as a part of the original draw 
of lakes for the national survey - the most of any of the lower 
48 states. The State then chose to add nine additional lakes 
(randomly selected) to the survey to yield the 50 lakes needed 
for statistically-based statewide estimates of lake condition. In 
addition to the 50 lakes, three reference lakes were later selected 
and sampled by USEPA as a part of the overall NLA effort. 


As part of its statewide assessment, Minnesota opted to add several measurements of unique interest 
to its overall state program. Examples of these add-ons are: pesticides; water mercury; sediment analysis 
of metals, trace organics and other indicators; macrophyte species richness; fish-based lake Index of 
Biotic Integrity (IBIs); and microcystin (at the index site and at a random near-shore site). A few of the 
findings are highlighted here. All of the reports completed to date can be found at: http://www.mpca. 
state, mn.us/water/nlap.html . 

Pesticides 


With the exception of the corn herbicide atrazine, pesticide degradates were more frequently detected 
than were the parent compounds. Possibly more of these parent compounds may have initially been 
present in a greater number of lakes, but had degraded prior to sampling. Alternately, parent compounds 
may have degraded early in the process, with degradates being subsequently transported to the lakes via 
overland runoff. Since the peak pesticide application period is late spring to early summer, mid-summer 
(July - August) lake sampling may have allowed ample time for degradation products to reach affected 
lakes. MDA was a key collaborator in this effort and conducted the pesticide analysis. 



70 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 








Detection of Pesticides and Pesticide Degradates in Minnesota Lakes 



Atrazine 

Deisopropyl- 

atrazine 

Desethy- 

atrazine 

Metolachlor 

Metolachlor 

ESA 

Metolachlor 

OXA 

Detection 

present 

non-detect 

present 

present 

present 

present 

Detection freq. 

87% 

2% 

64% 

4% 

27% 

7% 


Mercury levels 


Measurement of total mercury (THg) and methyl mercury (MeHg) concentrations indicate that 
high levels of THg and MeHg are distributed throughout the state. The northeastern region has higher 
THg and MeHg concentrations compared to the southwestern region, although the MeHg fraction may 
actually be somewhat higher in the southwestern region. Otherwise, high THg and MeHg concentrations 
are distributed throughout the range of NLA lakes. These data can be used as a baseline against which 
to evaluate the efficacy of mercury emissions controls in MN. The USGS was an important partner in this 
effort 

Aquatic Macrophytes 



Plant species richness was assessed at ten 
random near-shore sites on each lake. Generally, 
species richness increases from south to north 
peaking in the north central portion of the State 
before decreasing in the northeastern arrowhead 
region. The general trend of increasing species 
richness from north to south can be explained 
by water clarity, water chemistry, and human 
disturbance, and reaffirms previous observations. 
The decrease in species richness in the northeastern 
portion of the state can be attributed to tannin 
stained waters and rocky substrate associated 
with Canadian Shield lakes located throughout this 
region. 

Continuing Partnerships 

Minnesota also is collaborating on a regional 
assessment of lakes in the Prairie Pothole Region 
with the states of North Dakota, South Dakota, 
Montana and Iowa and EPA Regions V and VIII. This 
collaboration will expand applications of statistically- 
derived data and serve to enhance state, regional 
and national lake assessment efforts. 





National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 





























































































72 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 






CHAPTER 7. 


CHANGES AND TRENDS 



Photo courtesy of Great LaXes Environmental Center 


IN THIS CHAPTER 

► Subpopulation Analysis of Change - National 
Eutrophication Study 

► Subpopulation Analysis - Trends in Acidic Lakes 
in the Northeast 

► Sediment Core Analysis 


t' 









Chapter 7 


Changes and Trends 


Chapter 7 

Changes and Trends 

Among the long term goals of the National 
Aquatic Resource Surveys is the detection 
of changes and trends in both the condition 
of our Nation's aquatic resources and in the 
stressors impacting them. Trends in particular 
can be critical for policy makers i.e., whether 
policy decisions have been effective or 
whether a different approach is needed to 
achieve important water quality goals. 

This first survey of lakes and reservoirs 
provides clear information on current status 
and serves as the baseline for future changes 
and trends analyses. At this early stage the 
National Lakes Assessment is, however, 
able to incorporate three ancillary analyses 
to provide a cursory look at what changes 
have occurred. Over time, EPA intends to use 
further analysis and future surveys to start 
the trends analyses. 

The first indication of change comes from 
the analysis of a subset of lakes surveyed 
in the 1970s and again in 2007. Between 
1972 and 1976 the Agency and the states 
implemented the National Eutrophication 
Survey (NES) - a survey that included more 
than 800 lakes. The NLA was designed to 
allow for the comparison of some of the same 
lakes. 



The second example of change is based 
on data in a regional study of acidic lakes in a 
subpopulation of lakes, i.e., the northeastern 
U.S. Finally, a third examination of change 
involves the evaluation of cores from the 
lake sediments. By examining different cross 
sections within the sediment core and the 
microscopic diatoms present, analysts can 
infer past conditions in each lake. 

Subpopulation Analysis 
- National Eutrophication Survey 

Between 1972 and 1976, EPA conducted 
the National Eutrophication Survey. This 
study was designed to assess the trophic 
condition (defined as nutrient enrichment) 
of lakes influenced by domestic wastewater 
treatment plants (WWTP). The purpose of the 
survey was to measure nutrient inputs from 
all sources in the watershed relative to those 
of the WWTP source to determine if WWTP 
upgrades might be successful in modifying the 
lake or reservoir trophic state. While national 
in scope, it was unlike the NLA in that it was 
not probability-based. Instead it targeted 
a specific set of 800 wastewater impacted 
lakes. 

For the NLA, a subset of 200 lakes from 
the 1972-1976 NES survey was randomly 
selected using the same probability design 
principles from the broader survey. This 
allowed the condition of all 800 lakes from 
the original NES survey to be inferred from 



National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


74 
















Chapter 7 


Changes and Trends 


the subsample of 200 lakes sampled in 
2007. The phosphorus levels, chlorophyll-a 
concentrations, and trophic condition of 
the NES population in 2007 could then be 
compared to what was observed in the 1970s 
to determine how these metrics have changed 
over the last thirty-plus years. 

When making comparisons between then 
and now, some design differences between 
the two studies must be considered. NLA 
sampling consisted of a single, mid-summer 
integrated water sample at the deepest spot 
in the lake and from just below the surface to 
a depth of up to 2m (a sampling tube). The 
NES sampling consisted of sampling several 
sites on the lake as well as the inlets and 
outlets. NES sampling also included a site 
at the perceived deepest spot in the lake. 
Sampling was done with a depth-specific 
sampler (bottle) at just below the surface and 
at l-2m depth intervals. Analysts compared 
the integrated sample NLA chlorophyll 
concentrations and NES samples taken at the 
site nearest the NLA site and from depth(s) 
that most nearly mimicked the depth of the 
NLA integrated depth sample. The accuracy 


and precision of chemical analytical results 
were considered comparable to each other 
based on the methods and the quality 
assurance of both surveys. 

The NLA analysts looked at changes 
in the NES lakes over the past thirty-plus 
years using two approaches: by comparing 
concentration levels of key indicators and 
by examining trophic status. In both cases, 
researchers were able to estimate the number 
and percentage of NES lakes that showed 
a change since the original sampling in the 
1970s. It is worth noting that this type of 
analysis provides an estimate of net change, 
but little information on change in individual 
lakes. 

Phosphorus levels have decreased in more 
than 50% of the NES lakes (403) and for 24% 
(189) no change was detected. An increase 
in phosphorus levels was seen in 26% of the 
lakes (207) (Figure 34). 

Trophic status based on chlorophyll-a also 
changed (Figure 35). Trophic status improved 
in 26% (184) of the lakes, and remained 


Change in Phosphorus 
NES Lakes 1972 -2007 



Figure 34. Proportion of NES lakes that 
exhibited improvement, degradation, or no 
change in phosphorus concentration based 
on the comparison of the 1972 National 
Eutrophication Survey and the 2007 National 
Lakes Assessment 


Change in Trophic State 
(Chlorophyll a) 



Figure 35. Proportion of NES lakes that 
exhibited improvement, degradation, 
or no change in trophic state based on 
the comparison of the 1972 National 
Eutrophication Survey and the 2007 National 
Lakes Assessment. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


75 









Chapter 7 


Changes and Trends 


unchanged in over half (51% or 408 lakes) 
of the NES lakes. Trophic state degraded in 
23% (208) of the NES lakes. Specifically, 
using chlorophyll-a as the indicator of trophic 
state, 49% of the lakes (394 lakes) in NES 
were classified as hypereutrophic in 1972. In 
2007, that number had fallen to 35% (279) of 
the lakes. In 1972, just over 5% of the lakes 
were classified as oligotrophic and by 2007, 
over 14% of the lakes (117) were classified 
as oligotrophic (Figure 36). 

Subpopulation Analysis - Trends 
in Acidic Lakes in the Northeast 

A similar approach to assessing changes 
and trends was taken for lakes that are either 
acidic or sensitive to acidification as part of 
EPA's EMAP Temporally Integrated Monitoring 
of Ecosystems/Long Term Monitoring (TIME/ 
LTM) program. During the 1980s, the National 
Surface Water Survey was conducted on 
lakes in acid sensitive regions across the 
country. Again, EPA was able to make some 


comparisons. The NLA results show that 
acidification of lakes affects a very small 
number of lakes nationally. However, in 
certain regions of the country, the problem 
is of concern, particularly when lakes smaller 
than 10 acres (4 hectares) are included. 

Between the early 1990s and 2005, 
the acid neutralizing capacity in lakes in 
the Adirondack Mountains increased to a 
degree where many water bodies that were 
considered "chronically acidic" in the early 
1990s were no longer classified as such in 
2005 (Figure 37). Specifically, between 1991- 
1994 and 2005, the percent of chronically 
acidic waterbodies decreased in the 
Adirondack Mountains from 13.0% to 6.2%. 
Additionally, acid-sensitive lakes in New 
England were beginning to show a decrease in 
acidity. The percent of chronically acidic lakes 
in this region decreased from 5.6% in 1991- 
1994 to 4.3% in 2005. This trend suggests 
that lakes in these two regions are beginning 
to recover from acidification, though acidic 
surface waters are still found in these regions. 


National Eutrophication Survey Lakes 
1972 & 2007 


Oligotrophic 


Mesotrophlc 


Eutrophic 


Hypereutrophic 


20 


40 


60 


80 


Number of 
Lakes 



100 


Percentage of Lakes 

■■ 1972 - NES I I 2007 NES in NLA 

Figure 36. Percentage and number of NES lakes estimated in each of four 
trophic classes in 1972 and in 2007 based on chlorophyll-a concentrations. 


The trend of increasing ANC in lakes 
in the Adirondack Mountains and New 
England between the early 1990s and 
2005 corresponds with a decrease in 
acid deposition in each of these regions 
and reduced air emissions of the main 
components to acid deposition, which are 
sulfur dioxide and nitrogen oxides. 

Sediment Core Analysis 

In the third examination of change, the 
NLA incorporated paleolimnological analyses, 
a technique that uses lake sediment cores 
to obtain insights about past conditions. NLA 
analysts looked at thin slices of sediment 
cores and identified diatom silica casings. 
The community of diatoms present in 
each slice gives clues to the chemical and 
physical conditions in the lake when that 


76 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 



































Chapter 7 


Changes and Trends 


layer was deposited. Models have been 
developed to relate the diatom community 
to lake chemistry characteristics, such 
as total phosphorus, and to lake physical 
characteristics, such as clarity. Using these 
relationships, the diatoms in deeper layers of 
the sediment were identified and the chemical 
conditions present at that point in time 
were inferred. This technique was used very 
effectively during studies of acidification in 
lakes during the 1980s. Individual states and 
other organizations have also used sediment 
cores in this manner on more localized/ 
regional scales to improve our understanding 
of what lakes were like in the past. 


Percentage of Acidic Lakes 


Adirondacks 


New England 



EPA piloted this technique for application 
at a national scale to examine temporal 
change in a subset of lakes included in 
the NLA. In the field, the top layer of the 
sediment core was collected along with a 
layer deep in the core. Unfortunately, EPA 
was unable to date the sections of the core 
to confirm their age. Instead, NLA analysts 
used independent techniques, their own 
expertise, and the knowledge of regional 
experts to determine whether the cores 
were sufficiently deep for NLA purposes. The 
Agency acknowledges that this approach is a 
less reliable means of estimating the age of 
the cores. 



Slicing off the top layer of the sediment core for diatom 
analysis. Photo courtesy of Frank Borsuk. 


0 5 10 15 20 25 

Percentage of Lakes 

Figure 37. Change in percentage of chronically acidic lakes in the 
Adirondack Mountains and New England. 


For man-made lakes the bottom layer 
of the sediment cores was not collected 
because it was presumed sediment cores in 
these more recent lakes would not represent 
a pre-industrial condition. Three hundred 
ninety-two lakes, representing 34% of the 
target population, were in this category and 
also were not evaluated. In addition, 334 
lakes, representing about 22% of the target 
population, were not evaluated because 
the core length was insufficient. In the end, 
change estimates were possible for 426 lakes, 
representing 55% of the target population. 

Even though the percentage of target 
population is less than optimum, some 
information can be gleaned from the data. 
Results from the cores showed that an 
estimated 17% of lakes in the lower 48 states 
exhibited no significant change in inferred 
total phosphorus between the bottom of the 
core and the top of the core. A decrease 
in total phosphorus was estimated to have 



National Lakes Assessment A Collaborative Survey of the Nation's Lakes 


17 





















Chapter 7 


Changes and Trends 


occurred in 12% of the lakes while almost 7% 
of lakes were estimated to have experienced 
an increase in total phosphorus. The 
pattern in changes for total nitrogen differs 
somewhat. Nationally, the percentage of lakes 
showing no change between the top and 
bottom of the core is less than 5%. Sixteen 
percent of the lakes showed an increase in 
total nitrogen while 18% showed a decrease 
in total nitrogen. 

The difference between the top and 
bottom of the sediment cores suggests that 
many lakes may have lower total phosphorus 
and total nitrogen levels now than they once 
did. Without dating the cores, however, 
more information and analysis are needed in 
explaining these results. 



Photos courtesy of USEPA Region I 


While results from this approach are 
presented, further analyses will be necessary 
to determine if sediment core dating should 
be included in future lake surveys. Issues for 
consideration include evaluating: 

• Whether the approach used is sufficiently 
robust to identify cores reaching pre¬ 
industrial times across the country; 

• Whether the assessment of change 

in a relatively small subset of lakes merits 
the effort expended in the context of a 
national survey; and 

• Whether alternative coring and/or dating 
approaches should be considered for 
future iterations of the NLA. 



Measuring lake depth. 


78 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 










HIGHLIGHT 



Climate Impacts on Lakes 


Warmer Temperatures and Lake Condition 

The preponderance of information indicates that the planet is warming and significant changes in 
climate are expected around the globe. The International Panel on Climate Change (IPCC) unequivocally 
attributes the climate change to human activities that have increased greenhouse gases in the 
atmosphere. The United States alone saw an increase 
of 1° (F) over the last century. Most of the warming 
has occurred in the last three decades and the largest 
observed warming across the country has taken place 
in the winter months. In southern areas, surface water 
temperatures are surpassing those of air temperatures, 
while in the north, there is ample evidence of earlier 
ice-out dates. For lakes, these changes will impact 
reservoirs and drinking water sources, hydroelectric 
power facilities, irrigation regimes, shipping and 
navigation, and recreational opportunities. From an 
ecosystem standpoint, warmer lakes will result in 
changes in water depth, thermal regime, nutrient 
loading, retention time, mixing and oxygen availability, 
and suspended sediments - all of which will alter 
habitat suitability and lake productivity. 

Changes in the Upper Midwest — The Great Lakes 

While scientists generally agree that the nation will get slightly wetter over the next century, 
precipitation trends at a regional level are uncertain. In many areas, however, increased rainfall could 
be offset by increased evaporation, both in terms of soil moisture and surface water. The Great Lakes, 
which hold 18% of the world's fresh surface water, are being watched carefully. Many agree that warming 
trends throughout the region will lead to a climate more comparable to the Deep South thus making the 
lakes themselves smaller and muddier. Since 1988, temperature in Lake Erie has risen 1° (F) and while 
predictions vary, some researchers forecast that by 2070, lake level will fall about 34 inches and surface 
area will shrink 15%. This scenario would leave 2,200 square miles of new land exposed. Lower water 
levels and less ice cover will lead to more sediment delivery, and therefore more algae and potentially 
more waterborne diseases. Excessive algal blooms can affect aquatic life and harm animals and humans. 
Climate changes will also affect fish populations and zooplankton communities due to the disruptions in 
lake dynamics such as the timing and severity of ice-cover, winter-kill and spring/fall turn-over. 



Photo courtesy of Great Lakes Environmental Center 


* 


National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 


79 













Changes in the Southwest - Lake Tahoe and Lake Mead 


Persistent drought conditions, increased extreme rainfall events, more wildfires, and heightened 
flooding, runoff and soil erosion are all expected to afflict the already arid southwest. Since 1988, the 
average surface water temperature of Lake Tahoe has increased by 1° (F). Other signs of persistent 
warming are decreased snowfall, later snowfall, and earlier 
snowmelt. In Tahoe City, California, the percentage of precipitation 
falling as snow has dropped from 52% in 1910 to 35% in 2007 
and since 1961, peak snowmelt throughout the lake region has 
shifted earlier by two and a half weeks. In Tahoe: State of the Lake 
Report 2008, researchers reported that algal growth, considered 
an indicator of warming's acceleration, has increased rapidly with 
concentrations now five times what they were in 1959. Levels of 
nitrogen and phosphorus deposited from the Angora forest fire (also 
considered a climate indicator) also were 2-7 times greater than 
normal. 

Fluctuations in precipitation and snowpack have critical impacts 
on life in the desert. In Nevada, the water level in Lake Mead is 
steadily dropping and with it the hydroelectric production capacity 
by Hoover Dam. Studies cited by the National Conference of State Legislatures and Center for Integrative 
Environmental Research (2008) indicate that there is a 10% chance that Lake Mead could dry up by 2021 
and a 50% chance it will be dry by 2050. Lake Mead provides drinking water for over 2 million people 
and generates electricity for over 1.3 million. Water-based recreation brings in more than $1 billion to the 
area's economy. Major changes in annual precipitation and snowpack are proving difficult for reservoir 
managers who must balance winter flooding with maximum capture and storage for summer water needs 
— all within the context of overall declining water levels. 

What the Experts Say 

How a changing climate will impact the country's lakes is far from understood and not easy to grasp. 
The Climate Change Science Program, in its 2008 report, underscores that most observed changes in 
water quality across the continental U.S. are likely attributable to causes other than climate change and 
are instead primarily due to changes in pollutant loadings. Nevertheless, there is general agreement with 
the IPCC (2007) conclusion that higher water temperatures, increased precipitation intensity and longer 
periods of low levels are likely to exacerbate many forms of water pollution, with impacts on ecosystem 
integrity, and water system reliability and operating costs. Both groups agree that a mix of mitigation and 
adaptation will be necessary to address the impacts. 



Photo courtesy of Great Lakes Environmental 
Center 



National Lakes Assessment A Collaborative Survey of the Nation’s Lakes 









CHAPTER 8 

CONCLUSIONS AND IMPLICATIONS 
FOR LAKE MANAGERS 


IN 

► 

► 


THIS CHAPTER 

Overall Findings and Conclusions 
Implications for Lake Managers 




-v: ...» 




Photo courtesy of Great Lakes Environmental Center 




















































Chapter 8 


Conclusions and Implications for Lake Managers 



Photo courtesy of Jim Anderson and Dennis McCauley 


Chapter 8 

Conclusions and 
Implications for 
Lake Managers 

Overall Findings and Conclusions 

The NLA offers a unique opportunity to 
frame discussions and planning strategies 
based on environmental outcomes and across 
jurisdictional lines. It serves as a first step 
in the evaluation of the collective successes 
of management efforts to protect, preserve, 
or restore water quality. Attributable risk 
analyses can serve as a useful tool to help 
prioritize individual stressors. As EPA and its 
partners repeat the survey, the NLA will be 
able to track changes in water quality over 
time for lakes as a whole rather than just 
for a few individuals. This will help advance 
the understanding of important regional and 
national patterns in water quality, and speak 
to the cumulative effectiveness of the national 
water program. 


Taken together, the results of the 
NLA provide a broad range of information 
necessary to understand the condition of our 
nation's lakes and some of the key stressors 
likely to be affecting them. The results are 
especially important because they establish a 
national baseline for future monitoring efforts 
which can be used to track statistically-valid 
trends in lake condition. These stressors in 
lake systems are now placed in context of 
their relative importance for restoring and 
maintaining lake integrity. 

Condition of the Nation's Lakes 

The results of the survey provide 
information relating to the fundamental 
question of "what is the condition of the 
nation's lakes?" The NLA reports on condition 
in three important ways. Biological indicators 
are especially useful in evaluating national 
condition because they integrate stress of 
combined problems over time. The NLA 
shows that 56% of the nation's lakes are in 
good condition, 21% are in fair condition, 
and 24% are in poor condition based on 


82 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 





















Chapter 8 


Conclusions and Implications for Lake Managers 


a measure of planktonic O/E taxa loss. 
Recreational suitability is based on the algal 
toxin, microcystin. Microcystin was found 
to be present in approximately one-third 
of lakes and at levels of concern in 1% of 
lakes. Finally, trophic status results based on 
chlorophyll-a concentrations show that 20% 
of lakes are hypereutrophic, while 80% are in 
lower nutrient enrichment categories. 

Ecoregional assessments reveal broad- 
scale patterns in lake condition across state 
lines and across the country. Again using 
biological condition as the primary indicator 
of lake health, the Northern Appalachians, the 
Upper Midwest and the Western Mountains 
ecoregions have the greatest proportion of 
lakes in good condition - over half of the 
lakes in each of these regions are classified as 
good. 

While it is too early in the survey program 
to determine if overall lake condition is 
improving, NLA analysts were able to examine 
changes in one subset of lakes, first sampled 
more than thirty years ago. It is encouraging 
to see that trophic status improved in 26% 
of the NES lakes and remained unchanged 
in 51% of the lakes. This means that trophic 
status in over three-quarters of these lakes 
remained the same or even improved despite 
growth of the U.S. population. 

Major Physical and Chemical 
Stressors to Biological Quality 

The NLA results show that of the physical 
indicators measured in the study, degraded 
lakeshore habitat is the most significant 
stressor to poor biological integrity. Using 
this as the primary habitat indicator, just 
under half of the country's lakes (45%) are 
in good condition. The NLA results also show 
that lakes in poor condition for habitat are 
3 times more likely to be in poor biological 
condition. Another physical habitat indicator 


examined was the presence of human 
activities. From the standpoint of human 
disturbances along lakeshores, just one-third 
(35%) of the country's lakes are in good 
condition. Conversely, in addition to exhibiting 
good biological conditions, about half of 
the lakes in the relatively healthy Northern 
Appalachians, the Upper Midwest and the 
Western Mountains ecoregions, are in good 
habitat condition relative to other ecoregions 
across the country. 



About 40% of the nation’s lakes are constructed reservoirs. 

Photo courtesy of Eric Vance. 


Nutrients in the form of phosphorus and 
nitrogen are the second most important 
stressor to lake biological health. Fifty-eight 
percent of lakes are in good condition relative 
to total phosphorus levels and 54% are in 
good condition relative to total nitrogen. 

Lakes in poor condition for either of these 
stressors are twice as likely to be in poor 
biological condition. Yet, unlike habitat 
condition, nutrient levels vary widely across 
the country. The Northern Appalachians 
ecoregion has the greatest percentage of 
lakes in good condition relative to total 
phosphorus (TP) and total nitrogen (TN) 

(79% for TP and 88% for TN) while the 
Temperate Plains (38% for TP and 27% for 
TN) and the Northern Plains (22% for TP and 
9% for TN) ecoregions have the lowest. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


83 








Chapter 8 


Conclusions and Implications for Lake Managers 


Implications for Lake Managers 

While survey results fill key informational 
gaps in regional and national monitoring 
programs by generating estimates of the 
condition of water resources, evaluating the 
prevalence of key stressors, and documenting 
trends in the population of waters over time, 
they do not address all management concerns 
at all scales. For example, the lakes survey 
does not address causal factors or sources 
of stress. For water resource managers and 
city planners, efforts to reduce stresses and 
improve water quality entails confronting 
the source(s) of the stress (such as energy 
generation, agricultural production, or 
suburban development) and working toward 
implementing viable but often difficult 
solutions. 

Address Major Lake Stressors 

State lake management programs 
increasingly report that development 
pressures on lakes are steadily growing. 

The NLA findings show that local, state, and 
national initiatives should center on shoreline 
habitats, particularly vegetative cover, and 
nutrient loads to protect the integrity of lakes. 

The findings of the four physical habitat 
indicators show that poor habitat condition 
imparts a significant stress on lakes and could 
suggest the need for stronger management 
of lakeshore development at all jurisdictional 
levels. Of the four, degradation of lakeshore 
habitat cover is the most important stressor 
of lakes. The attributable risk analysis 
suggests that eliminating this stressor could 
restore the biological condition in 40% of 
lakes that are classified as poor, or 8.8% 
of lakes nationwide. Development and 
disturbance stressors along lakeshores (such 
as tree removal, residential construction, 
and grazing and cropping practices) impact 


the integrity of lakeshore and shallow water 
habitats, affecting terrestrial and aquatic 
biota alike. 

These NLA results support the continuing 
need for national, state, and local efforts to 
ameliorate the impacts of human activities 
in and around lakes to protect the lake 
ecosystem. For example, USDA's Conservation 
Reserve Enhancement Program supports 
the planting of buffers to serve as natural 
boundaries between water bodies and 
farm land. EPA's Low Impact Development 
(LID) program helps address lakeshore 
development pressures (see text box on page 
86 ). 

Nutrients have been a longstanding 
stressor of waterbodies in this country. 
Nationally, over 40% of the lakes exhibit 
moderate or high levels of nitrogen or 
phosphorus concentrations. In addition, 
regional hotspots are evident - in the 
Temperate and Northern Plains, nearly 
all lakes have high levels of nutrients. 

The NLA findings emphasize the need for 
continuing implementation of Federal-State 
partnership programs to control point and 
non-point sources of nutrient pollution. 

The NLA data can be used to support and 
enhance collaboration between jurisdictional 
authorities and the use of programs such as 
the Environmental Quality Incentives Program 
and Conservation Reserve and Enhancement 
Programs managed by USDA's Natural 
Resources Conservation Service, and the 
Section 319 Program and National Pollutant 
Discharge Elimination System run by EPA. 


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Chapter 8 


Conclusions and Implications for Lake Managers 


Track Status and Trends Information 

Lake managers should consider the 
national trend information as well as the 
ecoregional data in evaluating site specific 
information in a broader context. Conducted 
on a five-year basis, subsequent lake surveys 
will help water resource managers to assess 
temporal differences in the data and perform 
trends analyses. Future surveys will also help 
EPA and its partners evaluate national and 
ecoregional stressors to these ecosystems, 
track changes, and explore the relative 
importance of each in restoring or maintaining 
waterbody health. Wide-area or regional 
changes in stressors over time can potentially 
be linked to human factors such as land 
use changes (e.g., development) or natural 
causes (e.g., increased storm surges). 


Implement Statewide 
Statistical Surveys 

Statistical survey designs provide water 
resource managers and the public with 
consistent, statistically-valid assessments 
of the broader population of waters in the 
area of interest (nationally, state-wide, 
etc.) based on data from a relatively small 
representative sample. Information provided 
by these surveys can help managers monitor 
the effectiveness of their lake restoration and 
pollution control activities as well as target 
resources and additional monitoring where 
they are most needed. To date, 40 states 
are implementing statistical surveys (Figure 
38). These states are leveraging their limited 
monitoring resources to gain state-wide 
insights into their water resource quality. EPA 
encourages states to implement state-wide 
statistical surveys as a component of their 
CWA monitoring program. 


Use of Probability Surveys as a Component 
of State Monitoring Program 





** 

AK 

/O 

Hl & 


Status of State Use of Probability Surveys 

Adopted state scale survey (40) 
Piloting/Investigating use of state scale survey (7) 
Not currently pursuing state scale survey (3) 


August 25, 2009 

Figure 38. States with state-scale statistical surveys. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 





































Chapter 8 


Conclusions and Implications for Lake Managers 


Low Impact Development Protects Lake Quality 

Low impact development (LID) is a set of approaches and practices that are designed to reduce runoff 
of water and pollutants from the site at which they are generated. LID techniques manage water and water 
pollutants at the source through infiltration, evapotranspiration, and reuse of rainwater, preventing many 
pollutants from ever reaching nearby surface waters. LID practices include rain gardens, porous pavements, 
green roofs, infiltration planters, trees and tree boxes, and rainwater harvesting for non-potable uses such as 
toilet flushing and landscape irrigation. The primary goal of LID is to design each development site to protect, 
or restore, the natural hydrology of the site so that the overall integrity of the watershed is protected. 

Development typically causes an imbalance in the natural hydrology of a watershed by replacing pervious 
surfaces (e.g., fields, forests, wetlands etc.) with impervious surfaces (e.g., rooftops, parking lots, roads, 
etc.). This change in ground cover not only increases runoff because of decreased infiltration, it also reduces 
the potential for the removal of nonpoint source pollutants. 

By engineering terrain, vegetation, and soil features, LID practices promote infiltration of runoff close to 
its source and help prevent sediment, nutrients, and toxic loads from being transported to nearby surface 
waters. Once runoff is infiltrated into soils, plants and microbes can naturally filter and break down many 
pollutants and restrict movement of others. 

Implementing LID practices in watersheds will contribute to groundwater recharge, improve water 
quality, reduce flooding, preserve habitat, and protect lake quality. In addition, LID practices increase land 
value, aesthetics and recreational opportunities, and public/private collaborative partnerships while reducing 
stormwater management costs. For more information visit: http://www.epa.gov/owow/nps/lid. 


States with statistical survey programs 
are already using the results to develop 
watershed-scale or site-specific protection or 
restoration projects. Virginia, for instance, 
has established an intensive water quality 
monitoring program incorporating statistical 
sampling methods. South Carolina's 
monitoring program includes a statistically- 
based component to complement its targeted 
monitoring activities. Each year a new 
statewide set of statistical random sites 
is selected for each waterbody type, i.e., 
streams, lakes/reservoirs, and estuaries. 

The State of Florida also implements an 
annual probabilistic monitoring program. 

Their program will be an enhancement of its 
2000 Status Monitoring Network — a five-year 
rotating-basin, statistical design sampling of 


six water resources, including small lakes 
(1-10 hectares) and large lakes (>10 
hectares). Florida is currently in the fifth year 
of the Network and will report its findings in 
2010. 

State-wide surveys can be leveraged with 
the national survey and the information can 
be used in conjunction with other existing 
state monitoring programs to get a better 
understanding of the state's waters. In the 
same way that a lake association might relate 
the conditions it measures in a particular 
lake to other lakes, state/tribal managers can 
relate the conditions of lakes statewide to 
relevant ecoregional or national conditions. 
For example, Vermont compared its lakes' 
trophic status to the lakes in the Northern 
Appalachians ecoregion and nationwide 


86 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 











Chapter 8 


Conclusions and Implications for Lake Managers 


Results for Three Spatial Scales 
Trophic State 


Vermont 


Northern Appalachians 


US (lower 48) 



40 60 80 100 

Proportion of Lakes 

■H Oligotrophic (<= 2 ug/L) I . J Mesotrophic (>2-7 ug/L) 
i . . i Eutrophic (>7 - 30 ug/L Hypereutrophic (> 30 ug/L) 

Figure 39. Comparison of lakes by trophic state for Vermont, the Northern Appalachians 
ecoregion, and the Nation, based on chlorophyll-a. 


(Figure 39). This assessment shows that lakes 
in Vermont are more oligotrophic than lakes 
at the NLA ecoregional or national scale. Lake 
managers in states with a statistical survey 
network can use information such as this to 
target resources and management efforts. 

Incorporate New and 
Innovative Approaches 

EPA is encouraging states, tribes, and 
others to utilize NLA data and methods for 
their own customized purposes. The NLA 
provides lake managers with new tools and 
techniques to adopt into existing programs. 
Managers are encouraged to consider the host 
of new assessment indicators and methods 
that are applicable within assessment 
programs of any scale. For example, the 


quantitative assessment of physical habitat 
at the land-water interface is an area of 
intensifying focus within the lakes community. 
The NLA physical habitat assessment 
method provides a ready approach that has 
already been implemented by field crews 
across the lower 48 states and Alaska. The 
resulting data are readily reduced to four 
components of habitat integrity that relate 
directly to ecological integrity in lakes. For 
lake assessment programs lacking a physical 
habitat assessment component, the NLA 
method provides a low-cost and information- 
rich enhancement. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


87 

















Chapter 8 


Conclusions and Implications for Lake Managers 


The incorporation of recreational 
indicators within lake assessment 
programs can also yield useful information 
to lake managers. Public awareness 
of cyanobacteria and related toxins is 
increasing, fueled in part by an increasing 
number of beach closures and related media 
reports. In the NLA, while only a small 
proportion of lakes exhibited moderate or 
high-risk concentrations of microcystin, the 
proportions of lakes with concentrations 
of chlorophyll-a or cyanobacteria cells 
associated with the development of 
elevated microcystin was considerably 
greater. Routine monitoring of chlorophyll-a, 
cyanobacterial cell counts, and/or 
microcystin can be implemented using a 
tiered approach tailored to the likelihood 
of microcystin occurrence. Many states are 
now adopting such programs, resulting 
in greater protection of human health in 
instances where cyanobacteria blooms may 
limit or prohibit swimming. 


Work Beyond 
Jurisdictional Boundaries 

Survey data on a national scale allows 
for aggregation of data and comparability of 
the results across several ecoregional levels. 
Within each of these ecoregions, states 
often share common problems and stressors 
to shared watersheds. The NLA offers a 
unique opportunity for adjacent states to 
work together, establish coalitions, and put 
into place collaborative actions that cross 
state boundaries. As a starting point, EPA 
and its state partners are working together 
to develop approaches to monitoring that 
will allow comparisons on a state-wide basis 
and across state boundaries as well. EPA 
and the states are committed to finding 
mutually-beneficial and scientifically-sound 
ways to integrate and exchange data 
from multiple sources, as well as options 
to improve both sample collection and 
analytical methods. 



Aquatic weed harvesting is one way to manage plant growth. 

Photo courtesy of Frank Borsuk. 



Pennsylvania spillway. 

Photo courtesy of Frank Borsuk. 


88 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 













HIGHLIGHT 



State, Tribal, and Regional Lake Surveys: 
Examples From Across the Country 


State-wide Lake Assessments 

Oklahoma: Oklahoma was one of several states that chose to add to the number of nationally-selected 
lake sites within its boundaries to achieve a state-wide assessment. Oklahoma is looking into using 
National Lakes Assessment (NLA) survey data for further development of nutrient and biological criteria, 
incorporating new parameters into its established monitoring program, and nesting a probability-based 
survey into its fixed station rotation. 

Michigan: Twenty-nine Michigan lakes were randomly 
selected as part of the NLA. To allow for a state-scale 
assessment, the state added 21 additional randomly-chosen 
lakes. Michigan's surveyed lakes ranged from an unnamed 
10-acre lake in Clare County to 13,000-acre Gogebic Lake 
in Gogebic County. The state will continue to analyze its 
lake data set to further evaluate the condition of Michigan's 
inland lakes based on the national survey assessment tools. 

If 

Oregon: Oregon sampled 30 lakes across the state as 
part of the NLA. In Oregon, the results from the 2007 
NLA will help answer two key questions about the quality 
of lakes, ponds and reservoirs: What percent of Oregon's 
lakes are in good, fair or poor condition for key indicators 
of nutrient status, ecological health and recreation? What 
is the relative importance of key lake "stress factors" such 
as nutrients and pathogens? The random design took field 
crews to a wide variety of sites. Elevation at the target lakes 
ranged from 30 feet to 7,850 feet. Lake depths ranged from 
1 meter to 128 meters (Waldo Lake); maximum sampling 
depth, however, was 50 meters. The most difficult lake 
to reach was Ice Lake in the Eagle Cap Wilderness, which 
required the use of an outfitter and horses for the eight-mile 
and 3,300-foot elevation gain journey. 

Enhancing Lake Monitoring for the 
Lac du Flambeau Tribe, Wisconsin 

The Lac du Flambeau Tribe is using the NLA study to enhance its own water program. The ability to 
develop protective site-specific water quality criteria and assess lake health is limited when available data 
cover only a small geographic area such as the Lac du Flambeau Reservation. Participation in the NLA 
enabled the Tribe to compare Reservation lake data to national and regional lake health. The Tribe used 
the NLA protocols for physical habitat, water chemistry, and vertical water profiles on an additional 11 
lakes within the Reservation. These data are being entered into EPA's Water Quality Exchange (WQX) using 




Ice Lake in the Eagle Cap Wilderness. 

Photo courtesy of Oregon Department of 
Environmental Quality. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


89 








an Excel template to ensure data uniformity for comparison. The Tribe will develop lake report cards for 
the general public, managers, and decision makers assessing the health of Reservation lakes as compared 
to national and regional lake health. The Tribe will also be able to evaluate development of criteria using 
these data. 

Assessing Prairie Potholes: A Collaborative Effort. 

The Prairie Pothole Region crosses the north central U.S. and Canada and includes nearly 8,000 prairie 
pothole lakes. Prairie pothole lakes are intrinsically shallow and defined as natural lakes where 80% or 
more of the lake is less than 15 feet deep. Prairie Pothole 
lakes are part of a major waterfowl fly-way and are a 
valuable regional and national resource. In order to more 
fully understand this unique ecosystem, North Dakota, 

Iowa, Minnesota, South Dakota, Montana, USGS, and 
EPA undertook an assessment of these lakes. Analysts 
have found that nutrient and chlorophyll-a levels in Prairie 
Pothole lakes are quite high compared to the nation's 
lakes. A combination of high nutrient levels, elevated 
algae growth, low transparency, presence of roughfish, 
and broad, wind-swept basins serve to limit rooted plant 

growth. Maintaining rooted plant growth is important for . . 

Prairie Pothole health. More detailed information on the 
results of the Prairie Pothole survey will be provided in a 
NI_A supplemental report. 



90 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 









CHAPTER 9 


NEXT STEPS FOR 
THE NATIONAL SURVEYS 



IN THIS CHAPTER 

► Supplemental Reports 

► Tools and Other Analytical Support 

► Future National Assessments 









Chapter 9 


Next Steps for the National Surveys 



Photo courtesy of Lauren Wilkinson, Great Lakes Environmental Center. 


Chapter 9 

Next Steps for the 
National Surveys 

EPA is committed to continually enhance 
the National Aquatic Resource surveys in 
order to improve the quality and quantity 
of information it needs to understand the 
condition of the aquatic environment and 
how it is changing over time. As technologies 
advance, future surveys and collaborations 
can also lead to new indicators, new 
monitoring approaches, and new water 
resource management programs and policies. 

With the publication of this report, the 
lakes survey moves into a design/planning 
phase in preparation for the next survey in 


2012. This phase will incorporate lessons 
learned from the first lakes survey, other 
national surveys, and state, tribal and local 
experiences. Additionally, EPA anticipates 
that states and other partners will continue 
to utilize data from the first lakes survey and 
issue supplemental reports based on their 
findings. 

During 2010, EPA and its state and tribal 
partners will take stock of the survey and 
begin planning for 2012. Issues for discussion 
may include changes to the design, field 
methods, equipment, laboratory methods, 
and/or analyses procedures. Other items 
include improving reference site selection, 
refining regionally representative reference 
sites, and adding more reference sites to the 
survey. Consideration will be given not only 


Lakes 

2006 

2007 

2008 

2009 

2010 2011 

2012 

Design 

Field 

Lab and 

Data 

Analysis 

Report 

Design and 
Planning 

Field 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 























Chapter 9 


Next Steps for the National Surveys 


to how alternate approaches will improve 
future data, but how the Agency can ensure 
comparability to the initial baseline. 

Supplemental Reports 

The NLA included data collection for 
several indicators for which analysis could 
not be completed in time for this report. 

These included benthic macroinvertebrates, 
sediment mercury, and enterococcus. 

Analysts are currently developing 
macroinvertebrate indicators to add to our 
understanding of biological integrity of lakes. 
Sediment mercury samples are still in the 
data analysis phase, as is the enterococcus 
dataset. EPA plans to produce supplements 
to this report with the macroinvertebrate, 
sediment mercury, and enterococcus findings. 
Supplemental information will be posted on 
http://www.epa.aov/lakessurvev. 

In the next few years, EPA plans to 
continue additional analyses of the survey 
data to develop tools and strategies that will 
provide a better understanding of lakes and 
water resources in general. One important 
undertaking will be to conduct an in-depth 
analysis of the relationship between lake 
condition, stressors, and management actions 
such as point and nonpoint controls and other 
restoration activities. EPA plans to publish its 
progress and findings in interim lake survey 
reports. 

Tools and Other 
Analytical Support 

The next two years will also provide an 
opportunity for states to tailor their own 
statewide program to complement the 
national programs. Extensive discussion 
during the upcoming research and design 
phase will focus on ways to leverage and 
integrate national and state-scale surveys. 
This approach will improve the efficiency 


and value investment in monitoring. One 
EPA near-term project will be to work with 
the states to develop tools that can be 
used to re-create the survey for state-wide 
assessments and for customized purposes. 

EPA is committed to providing technical 
support to assist states, tribes and other 
partners in using these tools. Such an 
"assessment tool kit" might include IBI or 0/E 
model development, habitat data analysis 
techniques, decision-support tools, and web- 
based training sessions. 

Future National Assessments 

EPA and its state, tribal and federal 
partners expect to continue to produce 
national assessments on a yearly cycle. Rivers 
and stream sampling was completed in 2008 
and 2009 and a report will be released in 

2011. A national coastal assessment report 
will be published in 2012 based on field 
sampling in 2010. Wetlands will be surveyed 
in 2011, followed by a report in 2013. In 

2012, field sampling for lakes will occur again 
and the assessment report that follows in 
2014 will include an evaluation of changes in 
biological condition and key stressors. Each of 
the water type surveys will then continue with 
changes and trends becoming a greater focus 
for each resource type. 

The continued utility of these national 
surveys and their assessment reports 
depends on continued consistency in design, 
as well as in field, lab and assessment 
methods from assessment to assessment. 
However, the surveys should also provide the 
flexibility that allows the science of monitoring 
to improve over time. Maintaining consistency 
while allowing flexibility and growth will 
continue to be one of the challenges of the 
coming years. 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


93 







Chapter 9 


Next Steps for the National Surveys 


This national lakes survey would not 
have been possible without the involvement 
of hundreds of scientists working for state, 
tribal, and federal agencies and universities 
across the nation. Future National Aquatic 
Resource Surveys will continue to rely on 
this close collaboration, open exchange of 
information, and the dedication, energy, and 
hard work of its participants. EPA will continue 
to work to help its partners translate the 
expertise they gained through these national 
surveys to studies of their own waters. It also 
will work to ensure that this valuable and 
substantial baseline of information be widely 
used to evaluate the success of efforts to 
protect and restore the quality of the Nation's 
waters. 



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National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 



















Acronyms 


Acronyms 


ANC 

CPL 

CWA 

DO 

DOC 

EMAP 

EPA 

GIS 

IBI 

ITIS 

LDCI 

NAP 

NARS 

NES 

NHD 

NLA 

NLCD 

NPL 

O/E 

ORD 

OW 

PPR 

QA/QC 

QAPP 

qPCR 

REMAP 

SAP 

SPL 

TIME/LTM 

TMDL 

TPL 

TN 

TP 

UMW 

USDA 

USGS 

WMT 

WQX 

WWTP 

XER 


Acid Neutralizing Capacity 
Coastal Plains 
Clean Water Act 
Dissolved Oxygen 
Dissolved Organic Carbon 

Environmental Monitoring and Assessment Program 

Environmental Protection Agency 

Geographic Information System 

Index of Biological Integrity 

Integrated Taxonomic Information System 

Lake Diatom Condition Index 

Northern Appalachians 

National Aquatic Resource Surveys 

National Eutrophication Study 

National Hydrography Dataset 

National Lakes Assessment 

National Land Cover Dataset 

Northern Plains 

Observed/Expected 

Office of Research and Development, EPA 

Office of Water, EPA 

Prairie Pothole Region 

Quality Assurance/Quality Control 

Quality Assurance Project Plan 

Quantitative Polymerase Chain Reaction 

Regional Environmental Monitoring and Assessment Program 

Southern Appalachians 

Southern Plains 

Temporally Integrated Monitoring of Ecosystem/Long Term Monitoring 

Total Maximum Daily Load 

Temperate Plains 

Total Nitrogen 

Total Phosphorus 

Upper Midwest 

U.S. Department of Agriculture 
U.S. Geological Survey 
Western Mountains 
EPA's Water Quality Exchange 
Wastewater Treatment Plant 
Xeric 


National Lakes Assessment: A Collaborative Survey of the Nation’s Lakes 


95 





Glossary of Terms 


Glossary of Terms 

Acid Neutralizing Capacity (ANC): A lake's ability to adapt to, i.e. neutralize, increases in 
acidity due to acidic deposition from anthropogenic sources (automobile exhausts, fossil fuels) and 
natural geologic sources. 

Attributable risk: Magnitude or significance of a stressor. Is determined by combining the 
relative extent of a stressor (prevalence) and the relative risk of the stressor (severity). 

Benthic macroinvertebrates: Benthic meaning "bottom-dwelling". Aquatic larval or adult 
insects, crayfish, worms and mollusks. These small creatures live on the lake bottom attached to 
rocks, vegetation, logs and sticks, or burrow into the sediment. 

Biological assemblage: Key group or community of plant or animal being studied to learn 
more about the biological condition of water resources. 

Biological integrity: State of being capable of supporting and maintaining a balanced 
community of organisms having a species composition, diversity, and functional organization. 

Chlorophyll-a : A type of plant pigment present in all types of algae sometimes in direct 
proportion to the biomass of algae. A chemical indicator used to assess trophic condition. 

Complexity: Used to describe the diversity and intricacy of an ecosystem. A complex habitat is 
one that has a wide range of different niches for optimum growth and reproduction for both plants 
and animals. 

Condition : State or status of a particular indicator. For example, the biological condition of a 
lake is the status of a biological assemblage, such as diatoms. Often measured against a reference 
value or threshold. 

Ecoregions: Ecological regions that are similar in climate, vegetation, soil type, and geology; 
water resources within a particular ecoregion have similar natural characteristics and similar 
responses to stressors. 

Epilimnion : The uppermost, warmest, well-mixed layer of a lake during summertime. 

Euphotic zone: The uppermost layer of the lake defined as the depth at which light penetrates. 
Eutrophic: See Trophic state. 


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Glossary of Terms 


Eutrophication: The process of increased productivity of a lake or reservoir as it ages. Often this 
process is greatly accelerated by human influences and is termed cultural eutrophication. 

Hypereutrophic: See Trophic state. 

Hypolimnion : The lower, cooler layer of lake during the summer. 

Lakes Diatom Condition Index (LDCI): The sum of individual measures of a diatom 
assemblage, such as number and composition of taxa present, diversity, morphology, and other 
characteristics of the organisms. 

Limnological : Of or pertaining to the study of fresh waters. 

Littoral zone: The water's edge. The lake bottom extending from the shoreline lakeward to the 
greatest depth occupied by rooted plants. 

Macrophyte: Literally meaning "large plant." An aquatic plant that can grow emergent, 
submergent or floating. 

Mesotrophic: See Trophic state. 

National Hydrography Dataset: Comprehensive set of digital spatial data that contains 
information on surface water features across the U.S. 

Nutrients: In the context of the NLA, substances such as nitrogen and phosphorus that are 
essential to life but in excess can overstimulate the growth of algae and other plants in aquatic 
environments. Excess nutrient can come from agricultural and urban runoff, leaking septic systems, 
sewage discharges and similar sources. 

O/E (Observed/Expected) Ratio of Taxa Loss: A comparison of the number of taxa that 
are observed (0) at a site relative to the number of taxa expected (E) to exist for a site of similar 
nature. The taxa expected at individual sites are based on models developed from data collected at 
reference sites. 

Oligotrophic: See Trophic state. 

Pelagic zone: The open area of a lake, from the edge of the littoral zone to the center of the 
lake. 

Primary productivity: The production of organic compounds from atmospheric or aquatic 
carbon dioxide, principally through the process of photosynthesis. All life on earth is directly or 
indirectly reliant on primary production. In aquatic ecosystems, the organisms responsible for 
primary production are the phytoplankton, and form the base of the food chain. 


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97 






Glossary of Terms 


Probability-based design: A type of random sampling technique in which every site in the 
population has a known probability of being selected for sampling. Results from the sampled sites 
can be used to represent the population as a whole. 

Profundal zone: The deepest part of the lake. The lake bottom located below the depth of light 
penetration. 

Reference condition: The least-disturbed condition available in an ecological region, 
determined based on specific criteria, and used as the benchmark for comparison with the 
surveyed sample sites in the region. 

Regionally-specific reference: A subset of the reference condition based on reference lake 
sites of similar type and geography. For ecoregional assessments, the lakes are only compared to 
the particular reference lakes that are similar for that area. 

Relative extent: The relative prevalence of a specified condition (such as poor) for a stressor 
or biological indicator. A stressor with a high relative extent means that it is relatively widespread 
when compared to other stressors. 

Relative risk: The severity of the stressor. Like attributable risk and relative extent of the risk, 
this term is used to characterize and quantify the relative importance of the stressor. Stressors with 
low relative extent and high relative risk are called "hot spots". 

Riparian zone: The banks or shoreline of a lake or waterbody. 

Riparian or Shoreline disturbance: A measure of the evidence of human activities alongside 
lakes, such as roadways, dams, docks, marinas, crops, etc. 

Riparian vegetative cover: Vegetation alongside lakeshore. Intact riparian vegetative cover 
reduces pollution runoff, prevents streambank erosion, and provide shade, food, and habitat for 
fish and other aquatic organisms. 

Secchi transparency: A measure of the clarity of water obtained by lowering a black and 
white, or all white, disk (Secchi disk) into the water until it is no longer visible. Measured in feet or 
meters. 

Stressors: Factors that adversely affect, and therefore degrade, aquatic ecosystems. Stressors 
may be chemical (e.g., excess nutrient, pesticides, metals), physical (e.g., pH, turbidity, habitat), 
or biological (e.g., invasive species, algal bloom). 


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Glossary of Terms 


Stressor-response: Change in biological condition due to the presence of one or more 
stressors. 

Sublittoral zone: The lake bottom area between the littoral (rooted plants) to the depth at 
which there is no more light penetration. 

Taxa: Taxonomic grouping of living organisms, such as family, genus or species, used for 
identification and classification purposes. Biologists describe and organize organisms into taxa in 
order to better identify and understand them. 

Threshold: The quantitative limit or boundary. For example, an assessment threshold is the 
particular percentage of the reference condition or cut-off point at which a condition is considered 
good, fair or poor. 

Trophic State: Meaning "nourishment." Used to describe the level of productivity of a lake. 

Oligotrophic: A nutrient poor lake. Describes a lake of low biological productivity and high 
transparency or clarity. 

Mesotrophic: A lake that is moderately productive. 

Eutrophic: A well-nourished lake, very productive and supports a balanced and diverse array 
of organisms. Usually low transparency due to high algae and chlorophyll-a content. 

Hypereutrophic: Characterized by an excess of nutrients. These lakes usually support algal 
blooms, vegetative overgrowth, and low biodiversity. 

Watershed : A drainage area or basin in which all land and water areas drain or flow toward a 
central repository such as a lake, river or the ocean. 


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99 





Sources and References 


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